Barca, whose only previous home loss to English opposition was also to Liverpool in 1976, began strongly with Deco opening the scoring in the 14th minute via a header at the far post after a pinpoint cross from Gianluca Zambrotta on the left.
Zambrotta showed great pace to beat the Liverpool defence, and sent in perfect cross, leaving Deco to do the rest, beating diving Liverpool keeper Jose Reina.
Minutes later Deco almost had two, but Reina saved from close range, this time after good work from Lionel Messi on the right.
Liverpool settled, and it was Bellamy, a surprise starter after his bust up with Riise, who went close to equalising after 39 minutes when he headed into the side netting from a Steven Gerrard free kick.
But just before halftime the Welsh winger did have the ball across the goal line, executing a superb diving header from a Steve Finnan pass leaving Barca goalkeeper Victor Valdes trying to push the ball back into the field of play.
Bellamy, who doesn't have the best off-field record in football, then celebrated his goal with a fake golf swing, a tongue-in-cheek gesture in light of the fact that he apparently assaulted Riise with a golf club.
Fighters turn friends
The second half saw Liverpool much more organised in defence, with their back four assisted by midfielders Xabi Alonso and Mohamed Sissoko, as Barca were increasingly frustrated in front of their 93,000 home fans.
The crucial second goal came in the 74th minute after Liverpool striker Dirk Kuyt had his close-range effort only partially blocked by Valdes, with Bellamy ironically setting Riise up to smash the ball into the back of a vacant net.
"I think it was destiny for both of us," said Riise after the match.
"Both me and Bellamy had a hard run up to this game. However we put this (the bust up) behind us very early on," added the Norwegian international.
The defeat was Barcelona's first at the Nou Camp in any competition this season and their first in the Champions League since April 2003.
Draws set up tight ties
The other three Champions League fixtures on Wednesday all produced stalemates with Valencia twice fighting back to draw 2-2 with Inter in Milan, Chelsea coming from a goal down to match Porto 1-1, and Roma and Lyon going scoreless in Rome.
Valencia's David Silva, right, celebrates his goal
as Inter's Maicon looks on in dismay [AFP]
Inter were left to rue their poor finishing after they allowed Valencia back into the match twice, as goals to David Villa and David Silva for the Spanish La Liga side cancelled out Esteban Cambiasso's first half header and Brazilian defender Maicon's cool finish for the home side at the San Siro.
Meanwhile at the Estadio do Dragao in Portugal, Raul Meireles put the home side in front after an excellent strike gave Chelsea keeper Petr Cech no chance in the 12th minute, with defender John Terry receiveing treatment on the touchline.
Terry was stretchered off with what appeared to be a serious injury, but that didn’t dampen the visitors' spirits as striker Andriy Shevchenko equalised four minutes later after good work by substitute Arjen Robben.
"We had to change the system completely because we lost a lot of things when John Terry went off," said Chelsea manager Jose Mourinho.
"Michael Essien had to play central defence because we didn't have another option and as he is the heartbeat of the midfield that unbalanced us in terms of service.
"We got a draw and that is a good result."
Record number of bookings
Finally in Rome, the rain may have played a part in Roma and Lyon's drab 0-0 draw, but English referee Mike Riley also had his input in handing out a Champions League record of 11 bookings in a match dominated by fouls and diving.
"In the second-half we lacked a bit of freshness up front but I am proud of the players," said Lyon manager Gerard Houllier.
"I would have preferred 1-1 but we will be back at the Gerland (Lyon's ground) and it will be for us to run the match."
The second legs of all four ties will be played on March 6.