Chelsea advanced to the second round of the Champions League despite losing to Werder Bremen 1-0 Wednesday in Group A.
Both Chelsea and Bremen have 10 points, but the English champions lead the Germans on head-to-head. Bremen can still clinch if it gets at least a draw at FC Barcelona in its last group match.
Barcelona beat Levski Sofia 2-0 in the other group match to move to eight points.
Per Mertesacker scored the lone goal for Bremen with a 27th-minute header.
When Mertesacker leaped to meet Torsten Fring's twisting corner for his first Champions League goal, neither the nearby Didier Drogba nor Michael Ballack marked him.
Bremen had dominated from the start of the match through Mertesacker's goal, while Chelsea played like a team that may have been looking ahead to Sunday's showdown against English Premier League leader Manchester United.
In the second half, the English team attacked, but few chances were dangerous except forward Andriy Shevchenko's precise 70th-minute free kick, which forced the Bremen goalkeeper into a leaping dive.
