Frank Lampard put Chelsea ahead of Valencia in the 56th minute of their Champions League football match at the Mestalla but the London club later gifted the Spaniards a 1-1 draw after a conceding a late penalty.
Chelsea top the group with four points from two matches, with German side Bayer Leverkusen in second on three points thanks to their 2-nil win at home to Genk.
Two early goals helped injury-hit Arsenal to a 2-1 victory over Olympiakos although the north London club's fragile confidence was often exposed by the Greek side in an entertaining Group F clash.
Holders Barcelona barely paused for breath in a ruthless 5-nil hammering of BATE Borisov while former champions AC Milan took their time to get started before overcoming new boys Viktoria Plzen 2-nil at the San Siro, Milan.
Russian champions Zenit St Petersburg battled back from a goal down to record a 3-1 win against 10-man Porto in their Group G clash.
Surprise package APOEL Nicosia held Shakhtar Donetsk to a 1-1 draw at the Donbas Arena to move a point clear at the top of Champions League Group G.
Andre Ayew scored twice to help Olympique Marseille maintain their perfect Champions League start with a clinical 3-0 home win against Borussia Dortmund.