But Ten Hag confirmed in the build-up the Portuguese would remain captain if Harry Maguire was not on the field - and Fernandes repaid that faith with an outstanding contribution to a much-needed win.

It included his eighth goal of the season as he headed home Luke Shaw's 58th-minute corner.

"He was the best player on the pitch," said Ten Hag. "He played a little deeper role and he was brilliant, making the game from the back position, with a lot of good passes in between the lines. From there we created a lot of chances."

Ten Hag accepted Fernandes was not perfect. A late tackle on Betis' former Manchester City goalkeeper Claudio Bravo brought the midfielder a yellow card and did not look good.

But the United boss admitted it is a fine line Fernandes has to tread.

"His passion is his strength," added Ten Hag. "But sometimes he has to control that because when it's too much, it becomes a weakness. He knows that, but there are always small margins."

Fernandes ran away to celebrate his goal with his hands to his ears as the home fans chanted 'Bruno, Bruno' in his honour, showing they are behind him as well.

Marcus Rashford, Antony and Wout Weghorst were also on the scoresheet as United put themselves in a strong position to reach the last eight when the tie is concluded in Seville next week.

But Ten Hag knows one win alone will not banish the memory of Sunday's annihilation at Anfield, especially as he had been irritated by some of his side's performances preceding it, including the Carabao Cup final victory against Newcastle.

"We don't ignore it," he said. "We made mistakes and we got hammered. We showed complacency and you can never do that in top football.

"In the weeks before, I was not happy against Newcastle and the performance against Leicester in the first half, but sometimes you have to get the bad result where everyone opens their eyes."

United delight after 'unacceptable' Anfield debacle

In his programme notes, Ten Hag described the Anfield debacle as 'unacceptable' and said he had left his players in no doubt such performances would not be tolerated.

And, in a move that smacked of the Dutchman applying collective responsibility for the loss rather than singling out individuals for blame, he named an unchanged line-up.

For half an hour, all went well.

The hosts dominated as Rashford drove home his 26th goal of a magnificent season in the sixth minute after Fernandes' cross had been diverted into his path.

Further chances were created - the issue was none of them went in.

Bravo twice denied Rashford, Fernandes had a shot blocked and Weghorst's near-post effort was deflected wide even though he didn't get a corner.

Betis' form in La Liga, where they are fifth, suggested they were not as poor as it appeared and Ayoze Perez proved it when he drilled home a low shot from the angle of the penalty area.

Had the on-loan Leicester City forward got a second after he was set up by Juanmi - gifted possession by David de Gea, who rolled a pass straight to him from inside his six-yard box - anxiety might have spread through home ranks.

As it was, Perez's deflected shot bounced back off a post and United survived - although question marks remain over keeper De Gea, whose contract expires in the summer.

Pellistri shows potential in late show

Even Betis coach Manuel Pellegrini, who barely said anything noteworthy to the media during his three years as Manchester City boss, couldn't resist a pre-match dig at United after their seven-goal defeat at Liverpool.

As the weeks pass, it will be interesting to see if any individual does pay a price for what unfolded in what many view as the Premier League's greatest rivalry.

For now though, it can be claimed normal service has resumed.

Antony's superb curling shot restored the home side's advantage seven minutes after the restart and Weghorst found the net with a first-time strike eight minutes from time.

The key element of that late effort though was the contribution of Facundo Pellistri.

Good enough to play all three games for Uruguay in Qatar at the World Cup, the 21-year-old was only making his fifth United appearance, all off the bench.

But Pellistri's role in Weghorst's second United goal suggests he will be called upon more often as the campaign reaches its crucial phase.

Ignoring the safety-first option of a pass back to halfway, he took off on a run past the Betis defence to the byeline where he sent a cross back to Scott McTominay, whose effort was blocked and bounced kindly for Weghorst to finish.