“If they want to use the overtime (Thursday) night (as an excuse) then we are not mentally tough enough to be a winner,” said Boston head coach Doc Rivers after the Celtics lost 86-74 to the Raptors on Friday.

“If you’re tough then you come in and mentally grind this one out and win it too. If you are not then you use last night as an excuse.”

The loss in Toronto followed an overtime defeat to the Los Angeles Lakers at home on Thursday, a game that prompted head coach Doc Rivers to say: “We were awful.”

The frustrating thing for the Celtics is that before the two straight losses they were playing well, winning nine of 10 after a 5-9 start.

Rivers, who took a long time to meet the media on Friday, said their execution was poor again Friday, just as it had been on Thursday against the Lakers.

“I was really frustrated,” Rivers said.”We couldn’t even run a play out of a timeout so that’s frustrating. That’s focus or something. We have to fix that. We’ve been playing too well to go back down that road again. The last couple of games we turned back out of nowhere.”

Rivers was particularly irked on a play where one player did not know what he was supposed to do. “Two guys knew the play and one guy didn’t,” Rivers said. “That drains energy. Not being a professional drains energy.”

Rivers said he took so long to talk to reporters not because he was lecturing his players but because they were talking it out among themselves.

“We didn’t come out with the energy you need for a game like this,” said forward Paul Pierce who had 12 points. “We didn’t match their energy from the jump. They came out getting offensive rebounds and getting dunks. We just didn’t make the second effort I thought all night.

“I can’t put my finger on it. A lot of times Doc (Rivers) got mad in the first quarter because we just drew up a play and we come out and don’t execute it like we were supposed to.”

Kevin Garnett led Boston with 17 points in 28 minutes 44 seconds. It was only when he was in the game that Boston seemed to be cohesive.

But Pierce feels that the Celtics are not far from being a good team.