Barcelona fall to first defeat under Gerardo Martino against 10-man Ajax . FC Barcelona keep qualification hopes alive with 3 - 1 win over Napoli . Arsenal beat Chelsea 2 - 0 at Emirates Stadium . The Spanish side , who had a 100 % record in the group before Tuesday 's tie at the Petrovsky Stadium , took the lead with an Adrian Lopez goal in the 54th minute but a goalkeeping error by Thibaut Courtois 20 minutes later proved costly . Chelsea lose 1 - 0 to Basel in Basel but still qualify for knockout stages .
Barcelona fall to first defeat under Gerardo Martino against 10-man Ajax . FC Barcelona keep qualification hopes alive with 3 - 1 win over Napoli . Arsenal beat Chelsea 2 - 0 at Emirates Stadium . Chelsea lose 1 - 0 to Basel in Basel but still qualify for knockout stages .