Vela scored in the third minute when Theo Walcott passed the
ball into the six-yard box and the Mexico international slid in to tap past
Celtic goalkeeper Lukasz Zaluska.
Sagna scored with less than a minute to go before halftime with
a left-foot volley after a casual pass from Tomas Rosicky found him on the edge
of the area.
Nasri scored in the 51st from close range after Walcott set
him up inside the area.
Celtic, quiet for most of the match, staged a late rally by
pulling a goal back in the 73rd when Daryl Murphy slotted the ball past Arsenal
goalkeeper Manuel Almunia. Ki Sung-Yueng put Celtic within a goal of Arsenal in
the 82nd, scoring from close range off a low cross from the right.
Celtic was also awarded a penalty in the 68th after Jack Wilshere
pulled down Marc-Antoine Fortune but Georgios Samaras fired the ball well wide
of goal.
The Scottish team's only other clear chance before that came
from a free kick a few minutes after the first goal, but Almunia dived to his
right to catch the ball.
In the early match, Lyon's Jimmy Briand scored a late equalizer
to secure a 1-1 draw against AC Milan.
Lyon, Champions League semifinalists last season, dominated
the game but failed to take its chances. The French side fell behind when
Milan's Marco Borriello opened the scoring in the 55th.
Briand equalized when he converted a cross from Miralem Pjanic
with 10 minutes remaining.
On Saturday, Celtic rallied to a 2-2 draw with Lyon and Arsenal
drew 1-1 with AC Milan.
Arsenal manager Arsene Wenger used 18-year-olds Wilshere and
Emmanuel Frimpong in midfield for a second straight day after impressing
Saturday.
Wilshere played in central midfield and was involved in Arsenal's
first goal Sunday, passing from the edge of the area to Walcott, who set up
Vela. Wilshere nearly scored in the 35th when his fierce volley from the edge
of the area rattled the crossbar. He followed up and his header was saved by
Zaluska.
Frimpong, who is from Ghana, played in the holding midfield
role and pushed several Celtic players off the ball to win back possession.
Questions still remain over the future of Arsenal's midfield
star and captain, Cesc Fabregas. The Spain international returns to training on
Thursday after appearing in the World Cup final on July 11.
Wenger reiterated that Fabregas will stay at Arsenal despite
Barcelona's attempts to sign him, but urged his captain to commit publicly to
the Gunners.