Sekou Mara's double strike helped Southampton to a comfortable FA Cup replay win against Watford that sets up a tie against Liverpool at Anfield.
The French striker, who had been linked with a loan move in the transfer window, scored twice in the space of five minutes in the second half after a dour opening period.
Che Adams added a third to dispel any doubt in a game in which both managers made seven changes with promotion from the Championship being their priority.
Saints' club record-breaking unbeaten run - which stretches to 24 in all competitions - has moved them to second place in the Championship and into the last 16 of the cup.
The previous three meetings between these two teams had all ended in draws and it looked like this one was heading the same way as the changes disrupted the rhythm of both teams.
Ismael Kone came closest to breaking the stalest of stalemates, as Watford had five-on-four in a quick counter-attack, but his shot deflected off a defender's thigh and bounced off the bar.
Mara, hopeful of landing a place in France's Olympic team next summer, created Saints' best chance of the opening 45 minutes, finding Adams in space, but Watford keeper Daniel Bachmann thrust out a foot to block the striker's shot.
Mara took matters into his own hands in the 53rd minute as Southampton pieced together a trademark slick move.
Bournemouth loanee Joe Rothwell picked out Adams on the edge of the box and his touch round the corner freed Mara, who clinically found the far corner to break the deadlock.
Three minutes later he bettered that finish after Saints had surged onto the counter-attack, led by 17-year-old Tyler Dibling from his own half. His strong run scattered the Watford defence, he then fed Adams and when he moved the ball on to Mara, he crashed an unstoppable 20-yard shot past Bachmann.
After his two assists, Adams scored his own 10th goal of the season, making a near-post run to meet Rothwell's whipped free kick, and guiding the ball into the Watford net to ensure the trip to Anfield.
Southampton manager Russell Martin told BBC Radio Solent:
"We have a lot of games between now and (the trip to Anfield) so it won't be a focus for a while but I'm pleased for the lads as they've earned the opportunity with a really convincing performance in the second half.
"The biggest test for us will be to go there and be the team we want to be. We're not going to change anything. It's a brilliant challenge.
"I didn't enjoy the first half, it was probably as frustrated as I've been with them for some time. I'm not going to apologise for that because they've been so good, but we lacked aggression and intensity, which wasn't like us.
"In the second half they were amazing and everything we asked them to do wasn't technical or tactical, it was about mentality."
Watford manager Valerien Ismael told BBC Three Counties Radio:
"We dropped mentally in the second half but if you analyse the overview, tiredness was clearly there to see, because I didn't recognise my players in some situations - we lost the ball very easily, conceded yellow cards too easily and the decisions were too late.
"We were not able to step up in the second half, Southampton scored the first and second goals (quickly) and in the end we were lucky it was not more goals.
"We did the right thing in the first half as Southampton didn't have their fluid game, but after the first goal they were more fluid and it became more difficult - the heads and legs started getting heavy and then you start to make mistakes."