Joselu and Ayoze Perez scored in extra time as Newcastle advanced to the FA Cup fourth round with a 4-2 third-round replay win over Blackburn at Ewood Park.

The Magpies progressed to face Watford after Joselu struck just before half-time in the additional period – an effort it appeared should have been disallowed for offside – and substitute Perez added a powerful finish just after the interval.

Newcastle had gone 2-0 up early on via two 21-year-olds scoring their first goals for the club, Sean Longstaff netting with a deflected shot in the opening minute and Callum Roberts then marking his full debut with a 22nd-minute volley.

Blackburn responded impressively, with former Newcastle striker Adam Armstrong pulling a goal back in the 33rd minute and Darragh Lenihan levelling with a header in first-half stoppage time.

Isaac Hayden – brought on when half-time substitute Jamaal Lascelles went off injured just before the hour mark – went close to putting the visitors back in front in the second half of normal time when his header hit the post.

Newcastle, who had been winless in their previous six games in all competitions, will host the Hornets on January 26.

Three days on from the 2-1 loss at Chelsea that left his men 18th in the Premier League, Newcastle boss Rafael Benitez made eight changes to his starting line-up, the same amount he had for the original tie, the 1-1 draw at St James' Park on January 5.

The Spaniard, whose men have a crunch home clash with 17th-placed Cardiff on Saturday, retained only Matt Ritchie, Longstaff and Ciaran Clark from the team that started at Stamford Bridge.

Roberts was handed his first Newcastle appearance since making his debut – just over four years earlier, in January 2015.

Newcastle grabbed the lead with only 56 seconds on the clock when Longstaff collected the ball from Joselu, turned and struck an effort from outside the box that flew past David Raya via a deflection off Amari'i Bell.

Roberts tried his luck from a similar distance in the 13th minute, firing off-target, and Raya then saved Ritchie's shot with his legs as the away side's bright start continued.

Blackburn replied with a strike from Danny Graham – who was flagged offside – and deflected Richie Smallwood shot going wide, before falling further behind as Roberts joined Longstaff in opening his Newcastle account.

Jacob Murphy saw his shot parried by Raya, claimed the loose ball and delivered a cross which Roberts volleyed into the net.

Blackburn then reduced the deficit when Armstrong, who opted not to celebrate, beat Freddie Woodman having been played in by Graham.

Lenihan went close with a headed attempt two minutes later, before powering another in as he connected with Harrison Reed's corner just prior to the break.

Benitez brought Lascelles on for Clark at half-time – only to then be forced to take him off again soon after, with Hayden the replacement.

The manager looked distinctly unhappy as he spoke to the departing Lascelles, who it seemed was nursing a hamstring problem.

Ritchie had sent a fierce hit just over soon after half-time, and following an unsuccessful Joselu attempt, Hayden headed against the post.

After the game entered extra-time, Blackburn created a number of chances, with Bradley Dack failing to take the best one as he shot wide.

Newcastle then went 3-2 up in controversial circumstances, Joselu following up after Fabian Schar's shot was spilled by Raya, and the effort being allowed to stand despite the striker having looked offside when Schar hit the ball.

Perez then wrapped things up moments after the restart for the second period of extra-time, lashing a rising shot beyond Raya.