Third-choice goalkeeper Daniel Bachmann, making his first Watford appearance, was at fault for Tranmere's second goal, while debutant Mason Barrett's foul on Corey Blackett-Taylor led to the visitors' fairytale equaliser.

"The Premier League is our priority and I make no apologies for that," said Pearson.

"It was never my intention to do anything other than protect the squad, and look after what we need to do for the Premier League programme.

"I can't sit here and try to give you a feeling that everything is equal in terms of how we look at competitions. Unfortunately for us, the FA Cup is not the priority.

"If we were in a more comfortable situation and had more players available it would be different, but we don't because we have a lengthy injury list.

"We can't afford as a football club to put ourselves in a situation where we go into the league with even fewer players available. I have got to make decisions based on what is right for our season. It is as simple as that."

Watford, 231 days after they were thrashed 6-0 by Manchester City in last season's final, appeared on course to seal a comfortable route through to the fourth round after Tom Dele-Bashiru, making his full debut, Chalobah and Roberto Pereyra, later sent off, all scored inside the opening 34 minutes.

But Tranmere netted three times in 23 second-half minutes to secure the most unlikely of replays. VAR played its part for two of their goals.

Connor Jennings' header after 64 minutes was originally ruled out for offside before the decision was overturned. Manny Monthe capitalised on Bachmann's fumble to score the visitors' second.

Then, inside the final few moments, referee Graham Scott pointed to a Tranmere corner after he adjudged Barrett to have nicked the ball away from Blackett-Taylor. Television replays proved the youngster only took the man, with Mullin making no mistake by thrashing home the ensuing penalty.

"VAR is here and whether I agree or don't agree with it, doesn't really matter," added Pearson. "You get to half-time and when you are three-nil up you would expect to see it through."

Tranmere arrived at Vicarage Road following a 4-1 defeat at home to Coventry on New Year's Day which leaves them 21st in League One. Their stunning fightback here could provide them with the momentum to turn their league fortunes around.

"We were disappointed with the first-half display," said manager Micky Mellon. "We felt that we never laid a glove on Watford. It wasn't like us at all. It was almost as if we gave them too much respect.

"But then in the second half we said, 'come on, there are 2,500 travelling fans here and there is a lot of pride at stake'. We were a different team with more desire, more belief and produced an unbelievable result at a Premier League club."

Mellon joked: "The replay will not be an unnecessary distraction to the club's bank manager. We welcome it. We would like 10 replays."