European champions Barcelona led the charge of the fancied teams over the first obstacle of the Champions League course when they nearly all scored emphatic victories on Tuesday.
Barcelona thumped Levski Sofia 5-0 -- a sobering start for the first Bulgarian club to reach this stage of the competition -- for their biggest Champions League win.
Bayern Munich played superbly in the second half after a woeful opening 45 minutes to beat Spartak Moscow 4-0 at home, while AS Roma beat Shakhtar Donetsk 4-0 in Rome with all their goals also coming in the second half.
Chelsea beat Werder Bremen 2-0 in London with German national skipper Michael Ballack scoring his first goal for the club as he fired home from the penalty spot against his compatriots to seal the win.
Inter Milan, though, slipped up in Lisbon, losing 1-0 to Sporting and having Patrick Vieira sent off midway through the second half.
In the other games, Valencia beat Olympiakos Piraeus 4-2 in Greece in a match in which both teams led during the game.
Fernando Morientes, the former Real Madrid striker back in Spain after a short sojourn in Liverpool, scored a hat-trick for Valencia.
Two matches failed to end conclusively with PSV Eindhoven and Liverpool drawing 0-0 in the Netherlands while Galatasaray were held to a goalless draw in Istanbul by Girondins Bordeaux.
Matchday One will be completed on Wednesday with the remaining eight matches in the other four groups.
Fittingly, it was European champions Barcelona who scored the first goal of this season's competition proper following the qualifying rounds.
Andres Iniesta put Barca ahead after seven minutes and they went on to dominate not only the Bulgarians but also the elements in the Nou Camp.
Despite heavy rainfall throughout the match, Barcelona played superbly with Ludovic Giuly (39), Carles Puyol (49), Samuel Eto'o (58) and Ronaldinho, who scored in stoppage time, blowing Sofia off the park.
Bayern, European champions as recently as 2001 but who now regard themselves as also-rans in the competition because they cannot compete with the wealth of clubs in England, Spain, and Italy, showed Spartak Moscow they still know what European football is all about -- in the second half at least.
Claudio Pizarro set them on their way with a 48th minute strike while Roque Santa Cruz (52), Bastian Schweinsteiger (71) and Hasan Salihamidzic (84) wrapped up the victory.
AS Roma, who gained direct access to the group stage after being promoted to second place in last season's Serie A standings following the Italian match-fixing scandal, also did well in the second half against Shakhtar Donetsk of Ukraine.
They scored three goals in 12 minutes through Rodrigo Taddei, Francesco Totti and Daniele De Rossi before David Pizarro scored their fourth from long range a minute from time.
The night's major upset was in Lisbon where Inter, installed as Italian champions after Juventus were stripped of the title for their involvement in the scandal, lost 1-0 to Sporting.
The match was won and lost in a five-minute period halfway through the second half when Marco Caneira scored a stunning goal for Sporting and Inter midfielder Vieira was sent off on his European debut for his new club after his move from Juve.
Caneira scored a contender for goal of the season after 64 minutes as he chested down a high crossfield ball from defender Tonel, touched it past Maicon and unleashed a dipping volley from outside the box that went in off the underside of the bar.
Keeper Francesco Toldo leapt and managed to get a touch but failed to turn the ball over.
Vieira was sent off for head-butting Brazilian striker Liedson, the France midfielder's second bookable offence.
One of his old clubs, Arsenal, who reached the Champions League final last season, start their campaign at Hamburg SV on Wednesday.
The night's other games will include the all-British affair between Manchester United of England and Celtic of Scotland, AC Milan against AEK Athens and Olympique Lyon versus Real Madrid, eager to avenge a 3-0 loss to the French in the corresponding match a year ago.