Nine years since Guardiola and Mourinho's press conference battle

The Pep Guardiola vs Jose Mourinho rivalry escalated at a pair of press conferences held on April 26, 2011.

It was ahead of the Champions League semi-final first leg between Barcelona and Real Madrid, the usual press conferences were held the day before the match.

Mourinho fired his shot first, criticising for Guardiola for pointing to a correct offside call as an example of how close Barcelona had been to defeating Los Blancos in the Copa del Rey final that had been held a few days previously.

"Until now, there were two groups of coaches," Mourinho started.

"There was a small group that didn't criticise referees and then a big group, which I'm a part of, that criticised referees when important mistakes were made.

"Now, with Guardiola's comments, there is a third group and he's the only person in it.

"This group criticises the referee even when he gets it right."

Guardiola then fired back in the Bernabeu press room later that day.

"He is the f**king boss in this room and I don't want to compete at all at that," Guardiola said.

"We'll meet tomorrow at 20:45 on the pitch.

"Off the pitch, he has already won.

"I gift him that particular Champions League trophy for that."

It was the front page story the next day on MARCA, with the headline of "total challenge".

Guardiola went on to have the last laugh by winning that Champions League tie 3-1 as Barcelona went on to lift the Champions League again.