London - Cesar Azpilicueta seized on a defensive blunder and Juan Mata scored a slick second as Chelsea dumped Premier League leader Arsenal out of the League Cup with a 2-0 victory at its London rival on Tuesday.
The fourth round loss ends one route to a trophy for Arsenal manager Arsene Wenger, who failed to mastermind a victory over Jose Mourinho for the ninth time as he looks to deliver his club's first silverware since 2005.
Mourinho now has a quarter-final to look forward to in the competition that gave him the first trophy of his first Chelsea reign in 2005.
Manchester United will be joining Chelsea in the last eight after Javier Hernandez scored twice in a 4-0 victory over Norwich.
In a shock result, Fulham was beaten 4-3 by second-tier club Leicester. Stoke was forced into extra time against Birmingham but won 4-2 on penalties after it finished 4-4 over 120 minutes. West Ham also required penalties to see off lower-league opposition, but won 2-0 at Burnley with goals in regulation time.
At the Emirates Stadium, Chelsea was in action for the second time in three days, although only Gary Cahill survived the team that beat Manchester City on Sunday.
Wenger made eight changes for the side that won at Crystal Palace on Saturday to remain top of the league.
But in the cups, Arsenal has now lost twice in eight days, having been beaten at home in the Champions League by Borussia Dortmund last Tuesday.
A blunder at the back gifted Chelsea the opener in the 25th minute after launching a swift counterattack.
Arsenal defender Carl Jenkinson's backwards header was too weak to reach goalkeeper Lukasz Fabianski, and Chelsea defender Azpilicueta ran through and dispatched the ball into the net.
Arsenal rarely looked like equalising and Mata smashed the second into the roof of the net in the 66th after Willian nodded the ball back to the Spain midfielder in a move that started from a throw in.
It left the home crowd demoralised.
"Let's not go too quick for conclusions," Wenger said. "It's difficult to swallow what happened to us in the last week."
But asked about his poor record against Mourinho, Wenger quipped: "I don't think he scored the first goal."
At Old Trafford, United turned in the kind of performance missing largely in the league this season and Hernandez might hope for more game time up front after this double.
The Mexica striker opened the scoring from the penalty spot in the 20th after Leroy Fer fouled Adnan Januzaj. He was on target again nine minutes into the second half, heading home after Mark Bunn parried an initial effort.
Phil Jones volleyed in United's third, and Fabio da Silva collected a long ball from Wayne Rooney and slipped it past the onrushing Bunn.
In a seven-goal thriller at Leicester, it was a night to forget for Fulham.
Although Hugo Rodallega put Fulham in front, Wes Morgan, Chris Wood and Ignasi Miquel put Leicester 3-1 up by the 53rd.
Fulham staged a comeback through Rodallega and Giorgos Karagounis, who scored directly from a free kick in the 86th. But Lloyd Dyer restored Leicester's lead for good three minutes later.
At Turf Moor, West Ham left it late to see off Burnley thanks to two penalties.
Matthew Taylor scored the first in the 76th after Jason Shackell brought down Kevin Nolan, and Jack Collison netted in stoppage time after being fouled by Keith Treacy, who was sent off.