Young, who finished fifth in the Laser Radial at London 2012 last summer, dominated both of the day's races in the class to record two wins as did Weguelin and McIntyre in the women's 470.
Weguelin and McIntyre only began sailing together at the start of the year but appeared at home amid windy conditions with the former admitting to finding it easy in Majorca.
"It was pretty full on for the first day but good though. We were pretty fast on the racecourse so that made things quite simple and then we just played it quite simply," said Weguelin.
"We were just trying to do the basic stuff well. Obviously we're quite a young team so there's a lot to learn but everyone's quite supportive.
"I wouldn't say we've got huge expectations for this week but it's quite a new fleet so everyone's in the same boat. For us it's just about getting routines in place, seeing how it goes and learning."
Giles Scott also enjoyed success on his return to the Finn class, in which he is the world champion from 2011, with a first and second from his two races in Palma.
Scott, who was beaten to the sole British Finn place at the London 2012 Olympics by Ben Ainslie, took time out from the class while on America's Cup duty with Luna Rossa.
However he cruised to victory in race one and had a sizeable lead in the second only for a capsize to knock him back into second for second overall.
British team-mates Andrew Mills and Mark Andrews are in fourth and seventh overall respectively while the new men's 470 pairing of Luke Patience and Joe Glanfield finished third and second.
Patience, a silver medallist from London 2012 with Stuart Bithell, and Glanfield, a two-time Olympic silver medallist himself, only announced their partnership last month.
And Glanfield, who won Olympic silver with Nick Rogers at Athens 2004 and Beijing 2008, admitted the windy conditions were just what he needed on his first day's racing out of retirement.
"I can't believe it, our first day at a World Cup event and we get touching 25 knots at times. It was exactly what I was looking forward to about sailing again, and it all felt great," said Glanfield.
"We made a couple of mistakes and went for a little swim in the first race when we were winning but we got it back upright and back on track pretty quick.
"It wasn't without its teething problems but in the same breath we definitely had a pretty good day and we were fast so that was good."
Martin Evans took a victory and an 11th in the Laser while Young's British team-mate in the Laser Radial, Chloe Martin, was third and seventh herself.
Bryony Shaw, who won silver at the RS:X World Championships last month, was 12th and fifth and Sam Sills recovered from false start disqualification to place ninth in race two of the men's fleet.
Only one half of the 49er fleet managed to see any racing with Dave Evans and Ed Powys posting a win and a third while Dylan Fletcher and Alain Sign were third before tough conditions affected their second race.
British teammates in the 49er fleet Stevie Morrison and Ben Rhodes and the new pairing of Bithell and Chris Grube must wait until Tuesday to get their regatta underway.
The British crews in the new Nacra 17 multihull and 49er FX classes will also have to wait another day for their first taste of World Cup action due to testing conditions.