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Group E, Tuesday, 2:45 p.m. ET, Donbass Arena
Why it's big
These teams are tied atop Group E with four points from their opening two matches. This is the first of back-to-back matches between the two.
That means the winner Tuesday, if there is one, will have pole position in qualifying for the knockout stage. The return leg will be played Nov. 7 in London, and if Chelsea can win both matches, the defending European champions would be all but assured of progressing to the Round of 16.
One more factor complicates everything. The third-placed team in this group is Juventus, and up next, the Italian champions have back-to-back matches against Danish no-hopers Nordsjaelland (two losses by a combined 6-0 score so far).
Shakhtar and Chelsea must assume that Juventus will win both of those matches.
Chelsea, led by the creative spark of midfielders Juan Mata, Eden Hazard and Oscar, are off to a hot start in the English Premier League. This is the Blues' chance to duplicate that early success in Europe.