David Luiz sought out the Brentford substitute Jake Reeves to apologise to him in person after a reckless challenge had concussed the 19-year-old and forced him off in the closing stages of Chelsea's 4-0 FA Cup fourth-round replay win over the League One club.

The Brazilian cut across Reeves in the 86th minute and slammed his shoulder into his face. The referee Neil Swarbrick chose to book David Luiz and because Brentford had used all of their substitutes, they had to finish the game with 10 men.

Chelsea were value for the victory, which set up a fifth-round tie at Middlesbrough, and the David Luiz incident was unnecessary. The Chelsea defender Gary Cahill also came under scrutiny for an ugly 15th-minute tackle on Jonathan Douglas, from which the Brentford captain was fortunate to emerge unscathed.

"Jake is fine, he wanted to continue but our medical staff said it was better that he didn't," Uwe Rösler, the Brentford manager, said. "They said: 'Safety first.' I have not seen the situation clearly enough to make a statement now but the player [Luiz] came into our dressing-room and he spoke to Jake, which is a fantastic gesture. He apologised."

Was Reeves concussed? "Yes, definitely."

Rösler said that he had "no complaints" about Cahill's challenge and Rafael Benítez dismissed both of the flashpoints as "normal tackles, especially in a cup competition". The Chelsea manager was happier to talk up the patience and intensity of his players, after a scoreless first-half and how they came to show their ruthless side in front of the owner, Roman Abramovich, who attended his first game since 20 January against Arsenal.

Benítez was also pleased with the performance of John Terry, who marked only his third start since November because of a frustrating knee problem with the game's final goal. Benítez had suggested that Terry could not take a starting place for granted, that he needs to prove his fitness each week in training and thenovercome the competition for selection in central defence from Cahill, Branislav Ivanovic and even David Luiz, who played here as a holding midfielder. Terry said that the stipulations are normal and he would relish the challenge. "The manager knows me and I want to play," he said. "I have been out for months but the other two centre-backs have been doing well. It's good to have competition."

Rösler had one complaint and it related to the referee's decision to whistle for David Luiz's foul on Adam Forshaw in the 39th minute, on the edge of the Chelsea area, rather than allow play to continue. The ball ran on for Marcello Trotta, who shot into the net.

"I would not complain about the referee but we needed the margins on our side and they definitely weren't," Rösler said. "On a better day, he could have waited a few seconds and we could have been 1-0 up, which is what you need when you are massive underdogs. When the decision goes against you, you have no chance."