Updated

Lionel Messi scored a hat trick on Wednesday as Barcelona opened its UEFA Champions League Group G campaign with a comfortable 4-0 drubbing of Ajax at the Camp Nou.

Aiming for a better finish in Europe's most prestigious club competition after getting routed by current champions Bayern Munich in the semifinals last season, the hosts used some set-piece magic in the 21st minute to open the scoring as Messi whipped a beautiful free kick over the wall, off the inside of the left post and into the side netting for his first goal of the night.

After the break, the Catalans doubled their lead in the 55th minute when Messi collected a quick feed from Andres Iniesta and deposited his second goal of the match into the net 14 minutes later, Barcelona made it 3-0 off a well-executed set piece when Gerard Pique headed it home, and Messi completed his hat trick 15 minutes from time for his 62nd career Champions League goal.

Ajax had a chance to pull one back in the 77th minute, but Kolbeinn Sigthorsson's penalty kick low to the bottom corner was parried away by a diving Victor Valdes to preserve the clean sheet.

Elsewhere in the Champions League on Wednesday, FC Basel came away with a shock 2-1 victory over Chelsea at Stamford Bridge.

Oscar opened the scoring for the London club with a well-taken strike in the 45th minute, but Basel equalized in the 71st minute through a goal by Mohamed Salah. 10 minutes later, Basel netted the winner when Marco Streller found the back of the net.

The result snaps Chelsea's 29-match home unbeaten streak in Champions League group stage play.

Also in Group E, Atsuto Uchida, Kevin-Prince Boateng and Julian Draxler all scored second-half goals as Schalke cruised to a 3-0 victory over Steaua Bucuresti.

In Group F on Wednesday, Theo Walcott and Aaron Ramsey scored 20 minutes apart as Arsenal pulled out a 2-1 result over Marseille, while Napoli held on for a 2-1 win over 10-man Borussia Dortmund at the Stadio San Paolo.

Gonzalo Higuain struck first for Napoli in the 29th minute and the home side caught a break when Dortmund goalkeeper Roman Weidenfeller was issued a straight red card for playing the ball with his hand outside of the penalty area.

Lorenzo Insigne doubled Napoli's lead in the 67th and Dortmund got one back in the 87th through a Juan Zuniga own goal, but could not find an equalizer.

In Group H, Miranda, Arda Turan and Leo all scored as Atletico Madrid handled Zenit St. Petersburg by a 3-1 count, while a goal from Lucho Gonzalez was enough to push FC Porto to a 1-0 result against Austria Vienna.

In Group G's other tilt, Emilio Izaguirre was credited with an own goal on a deflected shot, and Sulley Muntari scored five minutes from time as AC Milan topped Celtic by a 2-0 score at the San Siro.