Arsenal lose, Chelsea win in UCL; Barcelona draw at Roma, Bayern stroll

Olivier Giroud was sent off for Arsenal as Arsene Wenger's men slipped to a 2-1 defeat in their Champions League Group F opener at Dinamo Zagreb on Wednesday evening.

The France international -- booked early on after an aerial challenge -- went close for the Gunners on 18 minutes as he saw a deflected header rebound off the post with Eduardo then blocking his close-range follow-up wide, but it was the hosts who took the lead.

Full-back Josip Pivaric made an overlapping run onto a fine through-ball, and though Ospina saved his initial effort, the ball rebounded off Alex Oxlade-Chamberlain into the net.

Giroud was dismissed five minutes from the interval for a second bookable offence, this time for a high challenge on Ivo Pinto, and the hosts extended their lead on 57 minutes -- Junior Fernandes heading home from a corner at the near post.

Theo Walcott came off the bench and took advantage of a high Dinamo defensive line to race onto a fine through-ball to slot past Eduardo to set up a tense finale, but the Gunners slipped to defeat.

Chelsea put their Premier League troubles behind them to cruise to a 4-0 victory over Maccabi Tel-Aviv in their Champions League opener at Stamford Bridge.

Chelsea were awarded a penalty after just five minutes when Predrag Rajkovic felled Willian in the box. The Maccabi goalkeeper was shown a yellow card, but Eden Hazard couldn't take advantage as he blazed over the bar.

The opening goal did come in the 15th minute -- and Chelsea needed a bit of luck. Willian curled in a free kick from 35 yards out looking for a teammate at the far post, the ball evaded everyone and bounced past Rajkovic and into the net.

Chelsea were awarded a second penalty which Oscar concerted, and any doubts over the result were ended in the 58th minute -- Costa superbly diverted Cesc Fabregas' ball into the box into the top corner, before the midfielder netted the fourth on 78 minutes.

Champions League holders Barcelona had to settle for a point with a 1-1 draw in their opening group game at Roma.

Barcelona took the lead 21 minutes in, with Luis Suarez beating the offside trap to head home Ivan Rakitic's deflected cross from close range.

Barca then thought they had a penalty in the 29th minute when Wojciech Szczesny appeared to bring Suarez down in the area, but the referee waved away the Spanish side's claims.

Roma then equalised a minute later with a quite astonishing goal from Alessandro Florenzi. He picked the ball up in his own half right by the touchline, crossed the halfway line and then fired in a shot which sailed over the head of stranded goalkeeper Marc-Andre ter Stegen.

Bayern Munich opened their 2015-16 Champions League account with a 3-0 win against Olympiakos in Piraeus on Wednesday evening courtesy of a Thomas Muller cross-shot, penalty and a late Mario Gotze goal.

The Bundesliga champions needed a bit of luck given Fernando Gago's impressive first-half performance, and got it as Muller's high cross from the right flank sailed over the Olympiakos keeper into the net on 50 minutes.

The visitors saw out the game as Gotze netted with a minute to go before Muller added his second from the spot, but will be concerned after Xabi Alonso -- Guardiola's main playmaker from deep -- picked up a knock in the second half.

Javier "Chicharito" Hernandez scored his first goal for Bayer Leverkusen as the Bundesliga side crushed BATE Borisov 4-1 in Germany.

Roberto Hilbert handed Leverkusen the perfect start, finishing superbly four minutes in with the outside of his right boot into the top corner from 15 yards out.

BATE equalised nine minutes later as Nemanja Milunovic's header was deflected past Leverkusen goalkeeper Bernd Leno, but Leverkusen took the lead through Hakan Calhanoglu after his 20-yard effort deflected wickedly up and over Sergey Chernik into the visitors' net two minutes after the restart.

Chicharito scored his first goal for his new club with a close-range finish on the hour, and the hosts then won a penalty after Calhanoglu's free kick was blocked by a handball, which the Turkey international clinically dispatched.

Gent fought back to clinch a point in a heroic display after having two men sent off in their first ever Champions League group match which ended 1-1 against Lyon.

The Belgian champions, who had Brecht Dejaegere and Thomas Foket both sent off in their Group H opener, fell behind to Christophe Jallet's second-half header but hit back through Danijel Milicevic's super strike.

Gent goalkeeper Matz Sels saved the day for the home side in the 88th minute when he denied Alexandre Lacazette from the penalty spot. as he lashed the ball across Anthony Lopes for the equaliser three minutes afterwards -- and Lacazette saw a late spot kick saved.

Russian champions Zenit earned a thrilling victory at Valencia as they survived a Spanish fightback to win 3-2 at the Mestalla.

Hulk handed Zenit the lead nine minutes in with a low finish across Valencia goalkeeper Jaume from 20 yards out and the Brazil forward then went one better, hitting a trademark piledriver from 25 yards with such stunning power that Jaume could do nothing about it despite the ball flying over his head.

Wednesday was a night for goalkeepers to forget, and Yury Lodygin -- who made a number of first-half errors -- was beaten far too easily at his near post by a low Joao Cancelo cross to half the deficit.

Lodygin's horror show continued as he allowed Andre Gomes' low effort from a tight angle to squirm underneath his body for the leveller, but his blushes were spared as Hulk turned provider to set up Axel Witsel for a fine 20-yard finish.

Porto and Dynamo Kiev shared the spoils in a 2-2 draw in their opening Champions League group opener in Ukraine.

The hosts took the lead 20 minutes in following a fine run from Denis Garmash, whose cross was eventually turned in by Oleg Gusev.

The visitors equalised soon afterwards with Vincent Aboubakar heading a fine goal following a Miguel Layun cross, and he added a second nine minutes from time after a goalkeeping error -- but Buyalskiy struck late on for the leveller.