Man City moved, and Liverpool responded, ensuring the Premier League title race goes to the wire.
Following City's three-goal comeback against Newcastle, Liverpool also fell behind early but came back to win on the season's penultimate matchday.
Now that the Reds are a point behind, both teams will try to beat the other on Sunday.
With a deflected strike 13 minutes in, Nathan Redmond put Southampton ahead and ended Liverpool's title hopes.
The hosts had their chances, but had to fend off waves of Liverpool pressure and attack.
Takumi Minamino scored for Liverpool after spending last season on loan at Southampton. After the break, Joel Matip looped an awkward but effective header into the net off a corner.
Jurgen Klopp has two finals to look forward to as Liverpool chases a quadruple: the Premier League against Wolves and the Champions League against Real Madrid. The only snag is that Man City must lose to give Liverpool a chance.
The Reds' second-string lineup rallies to win and keeps the title race alive. It's not Liverpool's best finish, but it'll do.