Gulf Today Report
Defending champions Arsenal were ousted by a rampaging Southampton after a 1-0 loss while West Ham advanced to the fifth round with a 4-0 win against third-tier Doncaster on Saturday.
The Gunners, who have clinched the title for a record 14 times, were dumped out of the tournament after an own goal by Gabriel handed Foxes a hard-fought win.
Brighton edged past Blackpool and Sheffield United beat Plymouth as the other Premier League teams in action avoided embarrassment against lower-league opposition.
Arsenal coach Arteta made seven changes from his team's 3-0 league win against Newcastle on Monday, with Pierre-Emerick Aubameyang and midfielder Emile Smith Rowe both absent.
Southampton's, who won the FA Cup in 1976, reaped the reward their positive approach deserved in the 24th minute.
Mohamed Elneny gave away possession on the edge of his own box and the ball was worked to Kyle Walker-Peters on the right.
The defender drilled the ball across the six-yard area and it was turned in by Gabriel -- the first time rejuvenated arsenal had conceded for 508 minutes.
Arteta, who won the FA Cup in August in his first season as arsenal boss, said he was "really sad" to exit the competition.
"We had a dream to do it again like last year and the dream today is over," he said.
"I am as well disappointed with the way we conceded the goal in an area where we know we shouldn't be doing that. At the same time I cannot fault the effort of the players." Pablo Fornals gave impressive West Ham an early lead at home to Doncaster as they dominated the League One side from the kick-off.
The home side doubled their advantage later in the first half when Andriy Yarmolenko pounced.
An own goal early in the second half from Andy Butler made it 3-0 and Oladapo Afolayan completed the rout.
West Ham, seventh in the Premier League after three straight wins, will play either Manchester United or Liverpool in the next round.
But Brighton did not have it all their own way against League One team Blackpool.