Marsh scored two of the visitors' five tries and was an impressive presence throughout as Denis Betts' men triumphed in the capital. The Vikings were forced to make do without two of their big-name signings, Gareth Hock and Kevin Brown, due to injury and installed former London loanee Joe Mellor at stand-off.
The Broncos elected to give a debut start to centre Alex Hurst, a close-season signing from Swinton. Last season's clash between the pair went right to the wire, with the hosts eventually prevailing thanks to a last-gasp Antonio Kaufusi try.
The visitors set about putting that right straight from the off, grabbing an early lead when Marsh took Jon Clarke's pass, cut inside and muscled over from close range. London really should have levelled things up moments later, but Jamie O'Callaghan was bundled into touch by a posse of Widnes defenders when he looked certain to score.
It was no-frills stuff from the Vikings, but their aggressive approach was certainly putting the Broncos on the back foot. And that energetic start was so nearly converted into more points on 16 minutes when Willie Isa was inches from grounding a teasing kick through.
The home side were showing precious little creativity, with loose kicks and passes into touch peppering their attacking play. But London were fronting up defensively, with the end result being both sides cancelling each other out for much of the opening half.
It was Widnes who were to move further clear on the half-hour, Clarke engineering space and romping over after neat hands from the Vikings backs. And the away side moved into a commanding position before the break, Dave Allen cashing in with a third try after the Broncos spilled an aimless kick on the last tackle.
With skipper Craig Gower departing due to injury, London were forced into a second-half reshuffle, Chris Melling and new signing Tommy Lee entering the fray. The Broncos had the perfect chance to grab a lifeline midway through the half, only for Will Lovell to somehow spill the ball in the act of grounding with the line at his mercy.
Tony Rea's men finally got on the board on 64 minutes, profiting from a loose pass that went to ground with Kieran Dixon scooping up and skidding home.
Further late scores saw Frank Winterstein rumble home for the visitors and Melling and Dixon burst over late on for the Broncos, Marsh rounding off the scoring.
Francis Cummins enjoyed a dream start to his role of head coach as new-look Bradford beat Wakefield 40-6 at the Provident Stadium.
Jamie Foster, Matty Blythe and Adam Sidlow all scored tries on debut as the Bulls, embarking on a re-building phase after almost going under last year, dominated the West Yorkshire derby from start to finish.
Foster, a specialist winger filling in at full-back, also kicked six goals from seven attempts to finish with a 16-point haul, while man of the match Jarrod Sammut helped offset the absence of the injured Luke Gale at scrum-half with a brace of opportunist tries.
Much was expected of the Wildcats, who won their last seven league games of 2012 to snatch the last play-off spot from the Bulls, but they could not match the energy and enthusiasm of Cummins' superbly-drilled outfit.
The visitors also sorely missed last year's player of the year Tim Smith, who is still recovering from an ankle injury sustained in a pre-season friendly, but coach Richard Agar will be alarmed at the ease with which their opponents broke through the heart of their defence.
The Bulls had a spring in their step from the kick-off and opened the scoring with a scintillating eight-man handling move. The lively Sammut made the decisive break and Foster handled twice before Chev Walker provided the final pass for winger Michael Platt, who crossed at the corner to make up for earlier dropping a tryscoring pass from Tom Olbison.
Foster then came up with the tryscoring pass for Blythe to go through a gap in the fragile Wakefield defence wide out, and Sidlow took Matt Diskin's short pass to crash over for Bradford's third try.
Foster kicked all three conversions to make it 18-0 and Bradford added a fourth try five minutes before half-time through the mercurial Sammut, who broke through the visitors' first line of defence and held off full-back Richard Mathers in a sprint to the corner.
Any hint of a Wakefield fightback was snuffed out within seven minutes of the re-start when Foster raced on to a grubber kick by Brett Kearney, who switched effectively from full-back to stand-off. He then jinked his way over for his second try and Foster's goal made it 34-0, but Wakefield avoided a whitewash when skipper Danny Kirmond blocked Sammut's kick and centre Dean Collis gathered the loose ball to race 70 metres for a try.
Former Bradford half-back Paul Sykes kicked the conversion but the Wildcats continued to spend most of the game penned inside their own half, and the Bulls rounded off the scoring with a seventh try from Kearney nine minutes from the end.
Laurent Frayssinous started his Super League coaching career with a win as his Catalan Dragons beat Hull KR 32-24 at MS3 Craven Park.
Frayssinous had the unenviable task of replacing Trent Robinson as the Dragons coach, but Robinson left the team in great shape after finishing fourth last season.The rookie coach reduced his pre-season to six weeks and that seemed to do the trick as Catalan started with a comfortable win.
One of the few bright spots for Rovers last season was keeping the French side to three tries or less in three close encounters, but Catalan scored four in the first half after Michael Dobson gave Rovers a third-minute lead with a penalty.
The lead only lasted four minutes as Thomas Bosc sent Zeb Taia over for a try and Bosc converted for a 6-2 lead which Jason Baitieri extended as he took advantage of some slack defending from Rovers.
Super League's oldest player Steve Menzies then rolled back the years with two tries in the closing stages of the first half.
His first came when Brent Webb's pass caught Rovers off guard on their left-hand side. The best try of the half came on the opposite flank when Jamal Fakir broke with electric pace before sending the 39-year-old Menzies away for a simple score. Bosc landed three of the four conversions as the home side struggled.
Rovers' problems worsened three minutes after the break. A breakdown in communication 20 metres from their own line between Con Mika and Lincoln Withers gifted Catalan possession from which Fakir ran through unopposed to score. Bosc missed the conversion but the Dragons led 26-2.
Rovers finally got over the Catalan line in the 51st minute from a superb offload from Cory Paterson. It was just what Rovers needed with half an hour to play and another Paterson offload helped set up Rovers' second try. A Dobson kick was dropped a metre from his try line by Webb and fell invitingly for Josh Hodgson to pick up and score. Dobson converted to make it 26-12.
Suddenly Rovers were on top and they made the most of their dominance when Omari Caro scored his side's third try of the game. Centre Liam Salter provided the perfect flick pass for the winger to score and Dobson converted to set up a tense finale.
However, Webb then secured victory for the Dragons with the killer try. Young prop Julian Bousquet powered through a gap in defence and offloaded for Webb to score. The game's final score came for the home side when Hodgson found Withers to open his account for the season with two minutes remaining. Dobson's conversion made the final score 32-24.
A stunning first half display by Super League favourites Warrington Wolves saw them kick off their 2013 campaign with a 40-24 victory over Castleford Tigers at the Halliwell Jones stadium.
The Wolves exploded out of the blocks and scored four tries in the opening 13 minutes through Chris Riley, Ryan Atkins, Rhys Evans and Richie Myler with Brett Hodgson landing three conversions to open up a 22-0 lead.
Further first-half tries from Ben Westwood and Garreth Carvell, both goaled by Hodgson, saw the Wolves extend their lead to 34-12 at half-time. The Tigers produced a much-improved second half display and restricted the home side to just a further score from Westwood but the damage had been done in the opening exchanges.
Castleford scored second half tries through Richard Owen and Jake Webster to add to first half scores from Justin Carney and Michael Shenton with Jamie Ellis landing four goals. Warrington coach Tony Smith had almost a fully fit squad to select from with centre Chris Bridge the only absentee as he recovers from a close season operation.
A much changed Castleford side saw coach Ian Millward give six full debuts to Jordan Tansey, Jake Webster, Keith Mason, Justin Carney, Weller Hauraki and Lee Gilmour, while Michael Shenton returned for his second spell at the club as captain but they were without winger Kirk Dixon who was ruled out with a torn calf sustained in training.
Chris Riley scrambled over in the corner after two minutes and three minutes later a superb midfield break by Simon Grix sent Ryan Atkins racing clear to score. Centre Rhys Evans claimed Warrington's third try on the 10 minute mark and three minutes later Richie Myler touched down with Brett Hodgson landing three conversions to make it 22-0 to the home side after just 13 minutes.
It was a surprise that it took a further 10 minutes for Warrington to add to their tally and this time a Briers bomb was kept alive superbly by Joel Monaghan and Evans to allow Westwood to cross for his side's fifth try which Hodgson again converted to stretch the lead to 28-0.
Castleford finally got a foothold in the game and were rewarded with points when Rangi Chase's kick deflected off Lee Briers and Jake Webster sent Justin Carney over for his side's first try of the season which Jamie Ellis converted.
Garreth Carvell added a further try for the Wolves which Hodgson converted, but the Tigers had the final say of the first half when Shenton pounced on a loose pass and raced 30 metres to score. Ellis kicked his second conversion to reduce the arrears to 34-12 at half time. Warrington were once again on the front at the start of the second half and three minutes after the restart Myler sent Westwood over for his second try of the game and Hodgson's conversion made it 40-12.
But to their credit the Tigers stuck to their task and produced a gritty second half display which was rewarded with tries for Owen and Webster and Ellis landed two more conversions but all the damage had been done in the first half.