MEMPHIS, Tenn. -- Just a few weeks ago, fans at the FedExForum booed Memphis Grizzlies rookie Nick Calathes. Not when he missed a shot or made a turnover. But when they saw him get up off the bench and head to the scorer's table to check into the game.

That was the low point. The back-up point guard was playing so poorly -- and so clearly without confidence -- that fans dreaded what would happen when he came in for starting point guard Mike Conley. But with Conley, who is also the team's leading scorer, out with an ankle sprain, the Grizzlies had little choice but to give Calathes the first NBA start of his career Saturday night against Milwaukee.

Calathes rewarded the Grizzlies with career highs 22 points, including four 3-pointers and five rebounds in a 99-90 victory over the Milwaukee Bucks on Saturday.

"The guy showed serious guts," Memphis coach Dave Joerger said after his team's sixth straight win and 11th in its last 12 games.

Memphis is an NBA-best 16-5 since Dec. 21.

Calathes played a career-high 40 minutes. And though he only handed out three assists, he did not commit a single turnover.

"That was the biggest stat of the night for me," Calathes said.

Memphis (26-20) also got another double-double from power forward Zach Randolph (23 points, 10 rebounds). Center Marc Gasol finished with 19 points and forward James Johnson chipped in 14 points off the bench and, as usual, put numbers all the way across the stat sheet with four rebounds, two assists and two blocks.

The Bucks double-teamed Randolph and left Calathes open from beyond the arc, where he hit 4-of-5 shots.

"I made them pay for it," Calathes said.

Calathes came to the Grizzlies in the offseason after spending four years in Europe. He struggled at times this season to even get the team into offensive sets and had been a 50-percent shooter from the free-throw line.

But teammates say they were not surprised he finally had a breakout game.

"He's here for a reason, because he's a good player," Gasol said. "It's not like it's his first year playing basketball. He's been doing this awhile."

Milwaukee (8-39) lost its sixth in a row and is now 1-15 in 2014. The Bucks have lost nine straight road games. They are 1-16 against Western Conference teams.

"I know that as a team we can do it," said guard Brandon Knight, who led the Bucks with 23 points and seven assists. "The good teams, they do it for four quarters."

The Bucks had a 69-67 lead after three quarters. But the Grizzlies went on a 16-4 run in the fourth quarter, capped by a Calathes 3-pointer with 6:23 to go up 83-73. The Bucks got the lead down to seven, but another Calathes 3-pointer with 3:12 remaining put Memphis up 90-78.

That was it.

"I don't know if it's the belief (is down)," Bucks coach Larry Drew said. "We just have breakdowns. And we didn't have those types of breakdowns in the first half. I have to get my finger on it and see what I can do about it."

Milwaukee forward Ersan Ilyasova finished with 14 points and 13 rebounds. Forward Khris Middleton scored 12, and center Larry Sanders and forward Caron Butler each had 10 points.

The Grizzlies shot 48.1 percent from the floor (38-for-79). The Bucks shot 39.5 percent (30-for-76).

Memphis out-rebounded Milwaukee 48-38.

The Bucks led by as many as 13 in the first half, going up 36-23 with 8:01 left in the second quarter. The Bucks led 49-43 at the break.

Calathes scored 12 of his points in the second half and was 3-for-3 from long distance. He also made two of his assists and a steal in the second half.

Conley is expected to miss no less than a week with the ankle sprain, and perhaps a good bit more time than that.

"Obviously, this game feels great," Calathes said. "I'll just do what I can do till Mike comes back and then I'll be back in the role I was."