In the running
Louis van Gaal's side just managed to take the three points, despite a relatively poor performance, when the Hornets visited Old Trafford in midweek. Stand-in captain Juan Mata just about secured the win seven minutes from time with a great free-kick.
Results elsewhere worked very well in United's favour, with both Tottenham Hotspur and Arsenal slipping up against West Ham United and Swansea City respectively, while Liverpool's 3-0 victory over fourth-placed Manchester City brought United level on points with their local rivals.
Wednesday's victory was United's fourth in a row, with others results seeing them reach the quarter-finals of the FA Cup and the last 16 of the Europa League, and now Herrera believes this has put United back in a position to win trophies.
The Spaniard told Manchester Evening News that the side are "showing passion" and showed that they can "fight to the end" on Wednesday, even when they don't "play good".
He continued, saying that he thought the team's attitude was "very good," adding that he remains "optimistic" as he thinks the side can still "fight for everything".
Room for improvement
Despite gaining the victory, United were poor on the night and Herrera was quick to admit to their short comings.
He said that they didn't "play well" and couldn't move the ball "from side to side" in the first 45 minutes, as well as giving up "some chances".
Herrera continued, saying that if United want to "win the race" for the top four, they need to learn to "win these sort of games." He thinks that their chances of doing that are "much better" with players like Mata too - someone he described as a player who can "make the difference".
Manchester United will travel to take on West Bromwich Albion at the Hawthorns on Sunday, March 6 with kick-off at 4pm BST.