Manchester City's stellar season gathered yet more momentum as the runaway English Premier League leaders reached the League Cup semi-finals with a penalty shootout victory at Leicester City after a 1-1 draw following extra time on Tuesday.

Arsenal, one of the sides trying vainly to catch City in the league, also battled into the last four by beating London rivals West Ham United 1-0 with a Danny Welbeck goal at The Emirates.

Pep Guardiola's City, even with a second-string team, maintained their 21-match unbeaten record in domestic matches this season, thanks once again in this competition to their reserve goalkeeper Claudio Bravo.

The visitors looked to have booked a semi-final place with a first-half Bernardo Silva goal until Leicester were awarded a soft looking penalty seven minutes into stoppage time which Jamie Vardy converted.

But after extra time produced no further goals, Bravo, their hero with two saves in a penalty shootout win over Wolverhampton Wanderers in the previous round, again delivered.

With City leading 4-3 in the shootout, Leicester's two big guns, second-half substitutes Vardy and Riyad Mahrez, who both helped change the game's momentum, surprisingly misfired.

Vardy's spot kick clipped the outside of the right-hand post before Mahrez's poor effort was saved by Chilean Bravo to clinch a City victory that utterly delighted Guardiola.

"I'm so happy," the Spaniard told Sky Sports after he had bounced on to the King Power Stadium pitch to congratulate his mixed bag of promising starlets and international heavyweights.

"A lot of young players played for us. They played real good," he said. "The way we had to react was not easy (after Leicester's penalty).

"We were tired, we had a lot of young players, and it's not easy because Jamie Vardy and Riyad Mahrez were there.

"What I liked the most is how we reacted and overcame that situation. It's a good indication for the future."

Guardiola had brought in some young blood, including Phil Foden, the teenager voted the Under-17 World Cup's best player in England's triumph, yet it was two of his big name recruits who dovetailed to put City ahead.

Ilkay Gundogan sliced through Leicester's midfield in the 26th minute before putting in Portuguese international Silva, who toe-poked home confidently.

The Foxes, who had also kept their luminaries on the bench, unleashed Vardy and Mahrez and started to look a match for City.

However, Guardiola was left complaining of an "unfair" finale when, with eight minutes added on, Demarai Gray tumbled in the box having barely been touched by fullback Kyle Walker.

Vardy put away the penalty with aplomb but when asked to do the same in the shootout both he and Mahrez were found wanting.

Arsenal manager Arsene Wenger, who replaced all 11 of his starters from the weekend Premier League home win over Newcastle United, still had plenty of international pedigree as England's Danny Welbeck got the winner three minutes before halftime.

Welbeck's persistence in bundling home from close range was one of the few highlights, a solitary shot on target, in a dull derby but David Moyes's side never threatened Arsenal, with a wayward Aaron Cresswell free kick proving their best effort.

With Arsenal and City progressing, there is the prospect of two mouthwatering last-four clashes because on Wednesday holders Manchester United visit high-flying Championship side Bristol City and Chelsea host struggling Bournemouth.