LONDON - Sergio Aguero scored a hat-trick as Manchester City escaped a huge FA Cup upset by coming from behind to win 4-2 at home to second-tier Watford on Saturday. Beaten Championship play-off finalists last season, Watford went 2-0 up inside 30 minutes through Fernando Forestieri and Troy Deeney to leave free-scoring City at risk of a shock defeat.However, Aguero struck three times in the last half an hour, with Aleksandar Kolarov also on target, to send last season's beaten finalists into the fifth round. With Watford 15th in the Championship, they were given little chance of pulling off an upset at the Etihad Stadium, but they took the lead in the 21st minute when Forestieri beat Costel Pantilimon. It was a reward for the visitors' bold start to the game and nine minutes later they made it 2-0, with Deeney finishing off a sweeping move involving Sean Murray and Ikechi Anya. City manager Manuel Pellegrini sent on defenders Vincent Kompany and Pablo Zabaleta for the second half and with half an hour remaining the hosts pulled a goal back through Aguero. The Argentine striker polished off a cross from Kolarov and in the 79th minute he plundered an equaliser, slipping the ball onto his left foot and curling home his 24th goal of the campaign.Watford were still within sight of a money-spinning replay, but with three minutes remaining Kolarov deceived visiting goalkeeper Jonathan Bond from 40 yards to make it 3-2 before Aguero completed his treble at the death. Liverpool also avoided a potential banana skin by winning 2-0 at second-tier Bournemouth. Beneath bright winter sunshine on the English south coast, Liverpool withstood an enterprising start from their Championship hosts before taking the lead in the 26th minute through Victor Moses.Daniel Sturridge made it 2-0 with half an hour remaining, running onto Suarez's dinked pass and tucking the ball past goalkeeper Lee Camp in front of watching England manager Roy Hodgson. Liverpool manager Brendan Rodgers praised his opposite number Eddie Howe for the way that Bournemouth had approached the game. "When you have a team that want to play football, they are the most courageous players on the field," he said. "It is easy to coach a team to sit back, not want the ball and defend, and then just wait for a hump up the pitch. Bournemouth are a very good side and I give credit to them first of all. Eddie is similar to myself in terms of the philosophy of football." Premier League Crystal Palace were the day's biggest casualties, losing 2-1 at holders Wigan, who were relegated to the Championship after stunning City 1-0 in last season's final. Ben Watson, who scored the winning goal at Wembley, set Wigan on their way in the 36th minute, with James McClean netting a 78th-minute winner after Aaron Wilbraham drew Palace level. Sunderland followed up their mid-week success against Manchester United in the League Cup semi-finals by toiling to overcome non-league Kidderminster Harriers 1-0, with Charis Mavrias scoring the only goal in the fifth minute. Swansea City, Cardiff City, Southampton and Hull City also overcame lower-league opposition, while Everton were due to visit third-tier Stevenage in the late game.