By Gary Washburn, Globe Staff

ISTANBUL -- After instituting some new offensive sets, Celtics coach Doc Rivers just allowed his team to freely scrimmage without many constraints Thursday. What's more, he allowed players such as injured guard Avery Bradley and reserve Dionte Christmas to draw up key plays for the White team (the reserves and camp invitees) against the Green team (the first eight players).

What resulted at the Darussafaka Spor Klub Dernegi was a competitive but lighthearted practice, followed by some fun with Turkish students at an NBA Cares event.

"I just wanted them to get up and down the floor," Rivers said. "I just walked around and watched."

The Celtics are preparing for Friday's preseason opener against Fenerbahce Ulker of Istanbul at the Ulker Sports Arena.

Rivers said he plans to play the starters about half the game; he wants his players just to compete and get accustomed to playing opponents again.

"The preseason game, if you win, that'd be great," said Rivers. "If you lose ... I don't want to lose. I'm just trying to get them ready for Miami [in the season opener]. As a player, you can't wait to play somebody else because when you call out the set, they don't know it."

The Celtics reserves were able to defeat the front-liners, 14-11, in the first scrimmage, a sign that the team is deeper.

"It’s good, because it’s only going to make us better," said Paul Pierce, referring to the strength of the reserves. "If you have a third team that can come out there and push the second unit and first unit, it’s only going to make your team better.

"Usually, your third team, that’s always getting blown out, losing every game, but that’s not going to be the case here. I think these guys have a great makeup. They’re going to be good for us throughout the year."

In the NBA Cares event, the Celtics held clinics with groups of kids.