Jayson Tatum said having fun was the key to the Boston Celtics' strong form after Thursday's 120-107 victory over the Memphis Grizzlies.

The Celtics moved to 38-27 as Tatum put on a 21-point fourth-quarter blitz, racking up 37 points overall on his 24th birthday.

His stellar showing was key as Grizzlies star Ja Morant impressed again, with 38 points, four rebounds and seven assists.

And Tatum, whose side sit fifth in the Eastern Conference, believes that embracing the fun factor has been crucial to the Celtics' promising season.

“I think watching us now, we play with a lot more passion,” he said. “We just seem like we’re having a lot more fun.

“This is basketball at the end of the day, and it’s supposed to be a lot of fun,” said Tatum. "And we've been having a lot of fun lately.”

Team-mate Al Horford cited the side's solid work on defense as the foundation of their success, with the Celtics boasting a defensive rating of 105.4 – second only to the Golden State Warriors.

However, he conceded there was still work to be done on the offensive front.

“Defensively, I feel like we know who we are,” Horford said. "On offense, I feel like we're continuing to find our identity and how we want to play and what we want to do.

"The more and more you start playing that way, it almost becomes second nature.

"We're not there yet, but I feel like we're making a lot of progress and it's going to be at the point that we're not even thinking about it and we're moving the ball, making the simple reads, and I feel like that's when we'll be at our best.”