Chelsea have advanced in the League Cup courtesy of a third penalty shootout success of the season while Arsenal had a smother path to the quarter-finals.
The Blues needed penalties to get past Southampton at Stamford Bridge after the game ended 1-1 in the 90 minutes.
Thomas Tuchel's side took the lead through a Kai Havertz header just before the break.
But Che Adams brought the Saints level inside three minutes of the second half after Chelsea keeper Kepa Arrizabalaga failed to hold a Kyle Walker-Peters drive and the Scotland striker converted from close range.
Arrizabalaga made amends late in the game with two fine saves as Southampton piled on some late pressure but the shootout belonged to the hosts.
Reece James slotted in the decisive spot-kick as Chelsea ran out 4-3 winners on penalties after Theo Walcott and Will Smallbone failed to score for the Saints.
Arsenal and Chelsea have advanced to the League Cup quarter-finals with victories over fellow Premier League sides Leeds United and Southampton on Wednesday, while third-tier Sunderland also progressed.
The Gunners eased through with second-half goals from Calum Chambers and Eddie Nketiah in a 2-0 win over struggling Leeds.
Chambers opened the scoring in the 55th minute, 23 seconds after coming on as a substitute.
The defender's header looked to have been saved by Illan Meslier but goal-line technology ruled that the ball had crossed the line.
The Gunners' second came in the 69th from a poor header back by Liam Cooper which left Meslier stranded as Nketiah rounded the keeper and his mis-hit shot from a tight angle just rolled into the corner.
League One Sunderland also enjoyed a shootout win, defeating Championship outfit Queens Park Rangers in London.
The North-East side won 3-1 on penalties after the game had ended goalless.
The quarter-final line-up will be completed when Manchester City continue their bid for a fifth straight League Cup title against West Ham, Burnley host Tottenham, Leicester play Brighton, Liverpool face second-tier club Preston and Brentford visit Stoke.
Australian Associated Press