London, Sept 28: Thierry Henry and Alexander Hleb scored in each half in Arsenal's victory.
Henry scored in the 38th with a rare header, and Belarus midfielder Hleb made it 2-0 in the 48th from 15 meters after clever passes from William Gallas and Henry.
Gallas limped off with a hamstring injury in the last few minutes, but manager Arsene Wenger was optimistic.
Arsenal, last season's runner-up to FC Barcelona, leads Group G with six points in two games. Porto has one point.
Brazilian defender Dudu headed in a 59th-minute goal in CSKA Moscow's 1-0 win against Hamburg. CSKA has four points and the Germans have lost their first two games.