Before returning to the top of the Premier League, Liverpool got to savor a Manchester United humiliation.
Now, unusually, Liverpool needs a swift recovery by its great rival after United's despair at being routed 4-0 by Everton on Sunday.
Liverpool's hopes of ending a 29-year English title drought could hinge on a big favor from sixth-place United when it hosts Manchester City on Wednesday.
After beating Cardiff 2-0 on Sunday, Liverpool is two points ahead of City with three games remaining. But Pep Guardiola's champions have a game in hand over Liverpool so defending the title is still under their control — unless they fail to beat United.
"If you are only motivated by winning the holy grail then something is wrong with you," Liverpool manager Juergen Klopp said. "We enjoy the ride together with our fans."
How his team could do with United holding City to a 0-0 draw just as it did when Liverpool visited Old Trafford in February.
"Man United was in that moment obviously in a much better moment," Klopp said. "We'll see what comes out on Wednesday. We have no influence on that, but we still have to play games after that."
For Arsenal, the challenge in its remaining four matches is sealing a top-four finish to qualify for the Champions League. That mission was hampered by a 3-2 home loss to Crystal Palace that left Unai Emery's side in fourth place but only ahead of Chelsea on goal difference and a point behind Tottenham.
Liverpool's breakthrough against relegation-threatened Cardiff only came in the second half — the sixth successive league game which Liverpool has won by scoring a winner after the break.
Georginio Wijnaldum met Trent Alexander-Arnold's corner at the near post in the 57th minute.
"The boys decided the routine for the first goal in the dressing room at halftime," Klopp said. "We had different routines but the players decided and I love that."
Liverpool was disrupted by losing Fabinho following a clash of heads and Milner was sent on to play what proved to be a decisive role.
Milner netted from the penalty spot in the 81st minute after Sean Morrison grappled Mohamed Salah, who fell to the ground.
"Morrison used his hands four or five times and (referee) Martin Atkinson took his time but eventually gave a penalty," Klopp said.
Liverpool now has a club-record 88 Premier League points, beating the 86 managed in the 2008-09 season. But there's still a first championship crown since 1990 to secure.
Cardiff's mission is staying in the Premier League and the south Wales side remains in the last relegation place — three points from safety with three games remaining.
Ole Gunnar Solskjaer apologized to fans after United lost for the sixth time in eight matches in all competitions — a spell that includes the manager's caretaker position being turned into a permanent job on a three-year contract.
Richarlison and Gylfi Sigurdsson scored before the break, and Lucas Digne and Theo Walcott added to United's pain with further goals in the second half.
"We have got to apologize to the fans because they were absolutely fantastic and that performance is not good enough for a Man United team," Solskjaer said. "All the way from me to the players, we know that we let the fans down, we let the club down. That performance is difficult to describe because it is so bad.
"We were beaten on all the things, all the ingredients you need, added to the talent. There is no place you can hide on the pitch."
United is where it was when Solskjaer replaced Jose Mourinho in December — sixth place.
United's loss meant Arsenal still ended Sunday in fourth place, two points ahead of Solskjaer's side despite the north London club's 10-match winning league home run ending.
After Christian Benteke netted his first goal in 20 games in the 17th minute, Mesut Ozil did level for Arsenal at the start of the second half.
But Benteke set up Wilfried Zaha to restore Palace's lead in the 61st before James McArthur headed in the visitors' third.
Pierre-Emerick Aubameyang scored in the 77th but Arsenal couldn't find two more goals to extend its 10-match winning league run at home.
"It was very frustrating, because it was a big opportunity," Arsenal manager Unai Emery said. "But we've had plenty of big opportunities before today, plenty of key moments that give us the opportunity to achieve our first target, to play in the Champions League next year."
That could still be secured by winning the Europa League with Arsenal facing Valencia in the semifinals.