The goal signaled a huge effort by Antic's team and Lehmann just managed to tip away a fierce shot from Edu in the 38th minute.
Celta almost took the lead immediately after the restart when captain Alexander Mostovoi headed onto the crossbar from Edu's cross from the left.
Reyes, Arsenal's recent big-money signing from Sevilla, came close to giving Arsenal the lead in the 54th minute when his shot was saved by the outstretched Cavallero. Thierry Henry sent the rebound wide from a good position.
Edu did better four minutes later when he doubled his tally with a swerving right-footed shot from the edge of the penalty area after evading Berizzo.
Celta drew deservedly level for the second time in the 64th minute when Jose Ignacio shot home from close range after defender Sergio Fernandez had headed on Mostovoi's corner.
But two minutes after Reyes was replaced by Nigeria forward Nwankwo Kanu, Pires grabbed Arsenal's winning goal in the 80th minute with a low close-range shot from Henry's pass.
Lokomotiv Moscow 2, Monaco 1
Marat Izmailov and Vladimir Maminov scored a goal each to lift Lokomotiv Moscow over Monaco 2-1 in a Champions League second round, first leg match.
Monaco's Fernando Morientes replied in the second half for Monaco, which may need the away goal when it hosts Lokomotiv in the second leg on March 10.
Lokomotiv, which hadn't played a competitive match since losing to Arsenal 2-0 in the Champions League group stage last December, was in control of the game in the first half.
Georgia international striker Mikhail Ashvetia nearly opened the scoring for the home side just four minutes into the game, but he failed to take control of an upfield pass from behind.
Twelve minutes later, Ashvetia missed a clear opportunity, firing over the crossbar from just 6m off another pass from behind.
His header off a left-wing pass from midfielder Sergei Gurenko went wide in the 25th minute.
Izmailov hit the target in the 32nd minute off a pass from Dmitry Loskov from the right. He dribbled past Monaco's Akis Zikos and Patrice Evra in the penalty box and left goalkeeper Flavio Rome no chance, firing into the right upper corner from close range.
Monaco's only chance in the first half came four minutes before the interval when Lokomotiv goalkeeper Sergei Ovchnnikov could not control the ball after Lucas Bernardi's powerful kick from outside the penalty box. But there were no Monaco players in the box to race to the opportunity.
Lokomotiv continued to control after the break and Loskov shaved the left post off a pass from Vadim Evseev in the 59th minute. Seconds later, Loskov and Evseev assisted Maminov to make it 2-0 for Lokomotiv.
Monaco narrowed the gap in the 69th, capitalizing on a mistake by Ovchinnikov, who left the goal to intercept Julien Rodriguez's header, but Rodriguez sent the ball into the ground and Morientes knocked it home.
Nigerian international striker James Obiorah silenced the 25,000 crowd at Lokomotiv stadium when he failed to beat Roma one-on-one in the fading seconds of regulation to improve Lokomotiv's chances in the second leg.
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