The Ospreys scored three tries in the last eight minutes to stun the Lions 28-38 in Johannesburg in their Challenge Cup clash on Sunday.
Oyonnax scored deep in injury time to seal a 28-27 victory over the Cheetahs in Saturday's Challenge Cup encounter in France.
The Cheetahs, Sharks and Lions have named their teams to do battle in the fourth round of the Challenge Cup this weekend.
A poorly disciplined Cheetahs outfit went down 33-20 to Pau in a Challenge Cup encounter at the NRCA Stadium in Amsterdam On Sunday.
Springbok stars Ox Nche and Makazole Mapimpi both scored twice while Lukhanyo Am also got on the scoresheet as the Sharks thumped Oyonnax 38-7 in Saturday's Challenge Cup clash in Durban.
The Lions picked up their second straight victory in the European Challenge Cup with an impressive 35-13 win over Newcastle Falcons at Ellis Park.