The pros and cons of a stuttering run-up are under debate after two crucial penalty misses in the Carabao Cup last 16.

Chelsea midfielder Valentin Barco missed the Blues' fourth penalty in their shootout defeat by Liverpool, which followed a 1-1 draw, when he hit the post after a stuttered run-up.

Xabi Alonso's side might have been in the EFL Cup quarter-finals had he scored, but they went out as defender Wesley Fofana sent one in sudden death high into the Kop at Anfield.

Barco's miss came after Arsenal midfielder Bruno Guimaraes had his spot-kick saved after a similar 'stutter' run-up as the Gunners crashed out against League Two Fleetwood Town on Tuesday night.

Both were shown how to do it by Liverpool defender Joe Gomez - a player who has never scored a senior goal in 319 professional appearances - who rifled the winning penalty into the top corner after a simple run-up.

Players opt for the stutter in a bid to trick the goalkeeper into giving them a clue as to which way they will dive.

The problem is it can backfire spectacularly if the goalkeeper holds their nerve or - in Barco's case - the taker fails to hit the target.

Former Chelsea defender Cesar Azpilicueta told ITV: "Every player picks his style where he feels confident, and for Valentin Barco, I believe that is his way of shooting it. I don't believe that was his first time, I hope not!"

The 'stutter' penalty became a theme of this year's World Cup. There were 26 at the summer's tournament but 11 were missed.

The stop-start run-up technique does not have a strict definition, but a player is allowed, under Fifa rules, to stop or feint in the run-up as long as they don't do it directly before kicking the ball.

Even Harry Kane tried it in the summer and missed. His stuttering run-up led to Croatia goalkeeper Dominik Livakovic saving his penalty in England's 4-2 win.

But because Livakovic came off his line early, Kane got a retake and smashed it home with a straightforward approach.

Arsenal and Brazil midfielder Guimaraes was one of those 11 to miss at the World Cup but did not change his approach at Fleetwood.

Some players have used it to their advantage. Brazil great Pele was famous for it while Cristiano Ronaldo has used it with both success and failure.

Manchester United's Bruno Fernandes, former Chelsea and Arsenal midfielder Jorginho and Wolves striker Raul Jimenez are others who often use the 'stutter' style.

"I wouldn't allow it if I was a manager," former Liverpool midfielder Danny Murphy told TalkSport on Wednesday after Arsenal's defeat the night before.

"It is ridiculous, self-indulgence, a player trying to be the centre of attention.

"When they do the stutter they think the keeper might go, but they aren't going that early, they aren't being tricked any more. It is naive."

But former Liverpool and Chelsea full-back Glen Johnson had a different view and pointed to the fact that Barco missed by mere inches.

"I like the technique," he told ITV. "It gives the players a bit of time.

"What confused me about that one [from Barco] is usually players are watching the keeper. He has moved, he has got it right and gone the right way but lifted it in the air for no reason.

"You have the whole goal to shoot at and that is the surprising part. He has already beaten the goalkeeper, he doesn't have to hit it into the top corner.

"If he puts that ball three inches to the right you would say it is the best penalty you have seen."

It will not go down as a goal in the record books but Gomez got the feeling of seeing one of his shots hit the back of the net for the first time as a senior player.

It is remarkable that in 319 games for Charlton Athletic, Liverpool and England, the 29-year-old defender has never got on the scoresheet.

But Gomez looked like a veteran finisher when he powered his penalty - which was the penultimate of the shootout before Fofana missed - into the top corner in front of the Kop.

"Everyone is on edge and we want to win," Gomez told ITV.

"For me it is the moment I was thinking about and anticipating. It was nice it went in."