Chelsea manager Jose Mourinho has retaliated after his Arsenal counterpart Arsene Wenger questioned his side's defensive tactics.
Wenger provoked the Blues boss this week, saying: "It is easy to defend."
Mourinho retorted by mentioning Arsenal's Champions League last-16 exit in February, saying: "It's not easy. If it was easy, you wouldn't lose 3-1 at home to Monaco."
The sides face each other in the Premier League on Sunday.

Will Wenger beat Mourinho this time?
Robbie Savage: "In 12 meetings in all competitions over the past decade, Arsene Wenger has never beaten Jose Mourinho. If you think about the type of football both teams have produced in the last few years under Wenger and Mourinho, you can understand why. In the past, the way Arsenal have played has suited Mourinho and Chelsea down to the ground because the Gunners have been cavalier going forward and left themselves wide open at the back."
Read more: 'Why Wenger can end Mourinho hoodoo'
Chelsea are 10 points clear at the top with six games remaining, and they will be champions if they beat Arsenal and Leicester in their next two matches.
The second-placed Gunners, meanwhile, have won their last eight league games.
Wenger and Mourinho clashed in last year's meeting at Stamford Bridge but the Blues boss played down their rivalry before their trip to the Emirates.
Mourinho said: "For me, he is not my rival. He is the manager of a big club in the same city where I work. It is a big club with the same objectives we have."
Mourinho said his relationship with Wenger was the same as he had experienced at previous clubs.
He added: "It is no different from when I was at Inter with the Milan manager, at Real with the Atletico manager, or Porto with Benfica. It was the same."
Mourinho called Wenger a "voyeur" in 2005 over comments the Frenchman had made about events at Stamford Bridge and last year described Wenger as a "specialist in failure".

Mourinho on Fabregas

Mourinho believes former Arsenal favourite Cesc Fabregas will receive a good reception on his return to his old club.
The 27-year-old midfielder joined the Blues from Barcelona in the summer.
"I'm not worried," said Mourinho. "Frank Lampard played for Manchester City at Stamford Bridge without any problem and with a good reception."
Fabregas had the option of returning to Arsenal when he left the Nou Camp.
"I know why he chose Chelsea, not why he didn't choose Arsenal," said Mourinho. "I can only talk about what we promised him, not his time at Arsenal or what stopped him going back.
"We promised him we would build a team adapted to his style of play and he would be an important part of our project."

Mourinho on Hazard

Chelsea forward Eden Hazard, who signed a new five-year contract in February, was this week praised by Real Madrid assistant manager Zinedine Zidane.
But Mourinho is confident the 24-year-old Belgium international, who is favourite for the players' player of the year award, will stay.
"He just signed a new contract," said the Portuguese. "We didn't put a gun to his head. He likes Chelsea. He likes the league and he has made a commitment to that.
"I don't think he is interested in going."