* Van Persie denies West Ham in 2-2 draw
* Newcastle lose 2-0 at second-tier Brighton
* Macclesfield upset Cardiff, Luton beat Wolves (Adds Man United win)
By Martyn Herman
LONDON, Jan 5 (Reuters) - Chelsea striker Demba Ba struck twice on his debut as the FA Cup holders enjoyed a 5-1 drubbing of Southampton in the third round on Saturday and Robin van Persie's majestic last-gasp equaliser salvaged a 2-2 draw for Manchester United at West Ham.
Senegal international Ba, signed from Newcastle United on Friday, scored the London side's equaliser and their fourth before Frank Lampard's late penalty took the midfielder to joint second on Chelsea's all-time scoring list with 193 goals.
United, 11-times FA Cup winners but not since 2004, were staring at a 2-1 defeat at Upton Park after Joe Cole marked his return to east London by setting up two carbon-copy headers for James Collins after Tom Cleverley put United ahead.
With 90 minutes on the clock, substitute Van Persie rescued his side by controlling a 40-metre pass from Ryan Giggs and dispatching a lethal shot past keeper Jussi Jaaskelainen.
"You never rule out fighting back with our team but certainly at 2-1 down with a couple of minutes to go you hope you get a break," United manager Alex Ferguson said.
"The manner of the goal, with Ryan Giggs's ball and Robin van Persie's finish, was world class."
While Ba began in style, the gloom remained at his old club Newcastle, who lost 2-0 at Championship (second tier) Brighton & Hove Albion - one of several upsets on the day when England's lower-ranked clubs traditionally take aim at the big boys.
Goals from Andrea Orlandi and Will Hoskins earned Brighton, runners-up to Manchester United 30 years ago, a repeat of their fourth-round victory over Premier League Newcastle last season, condemning Alan Pardew's side to an 11th defeat in 14 matches.
Cardiff City, runaway leaders atop the Championship, were the biggest victims, losing 2-1 at minor league Macclesfield Town, while former FA Cup runners-up Luton Town, now outside the Football League, beat visiting Wolverhampton Wanderers 1-0.
Several clubs struggling in the Premier League flirted with defeats against lower league opposition before earning replays.
Fulham were held 1-1 at home by second division Blackpool, Wigan Athletic needed a late equaliser in a 1-1 draw with third tier Bournemouth, and Sunderland recovered for a 2-2 scoreline at Bolton Wanderers, who lost their top-flight status last season.
Premier League Reading had to come from a goal down after one minute to beat third tier Crawley Town 3-1 away.
South coast seventh-tier minnows Hastings United, the lowliest survivors of the 758 clubs who began the 132nd edition of the world's oldest knockout cup competition in August, had their fairytale cut short in a 4-1 defeat at Middlesbrough.
Chelsea's Ba needed only 35 minutes to start justifying the seven million pounds fee British media reported Chelsea had paid for his services when he crashed the ball into the net from a position virtually on the goal-line after Juan Mata's chip.
Jay Rodriquez had given Southampton an early lead but once Ba levelled they were no match for Rafa Benitez's side. Victor Moses made it 2-1 just before halftime and Branislav Ivanovic put Chelsea in control with Ba and Lampard adding some gloss.
Chelsea, bidding for a fifth FA Cup triumph in seven seasons, continued their unbeaten sequence in the FA Cup third round, which now stretches back to 1999, while their last defeat in the competition - other than in a penalty shootout against Everton in 2011 - was five years ago against Barnsley.
"It is always important for a striker to score goals but more than just the goals was his contribution for the team," Chelsea boss Rafa Benitez said of Ba.
A day after completing his move from Liverpool and 10 years since leaving West Ham for Chelsea, Cole looked like he had never been away as he sparkled on his old Upton Park stage.
After Cleverley's classy finish put United in front after 23 minutes, Cole delivered an inswinging cross for Collins to head an equaliser four minutes later.
West Ham's second goal after 59 minutes was similar, Collins again connecting sweetly with Cole's teasing delivery.
Van Persie deprived Cole of the headlines, however, taking down Giggs's sublime pass with his left foot before finishing with his right for his 20th goal since joining from Arsenal in August.
Manchester City's Mario Balotelli was a late substitute in their 3-0 home win over Gianfranco Zola's Watford, a day after the controversial Italian striker was splashed across British newspapers grappling with manager Roberto Mancini.
Goals from Carlos Tevez, Gareth Barry and Marcos Lopez eased the English champions into the fourth round.
Tottenham Hotspur's fine form continued with Clint Dempsey scoring twice in a comfortable 3-0 home win over third tier Coventry City, the side they lost to in the 1987 FA Cup final.
While hardly in the same league as some of the great FA Cup shocks, Macclesfield took the prize for the day's biggest upset, bridging a gap of 82 rungs on the English football ladder to stun Cardiff with Matthew Barnes-Homer's late double.
Minor league Mansfield Town have a chance to upstage Macclesfield when they host Liverpool on Sunday.
(Reporting by Martyn Herman, edting by Ken Ferris and Stephen Wood)