BOSTON – With the clock ticking on his team, Timberwolves point guard Ricky Rubio calls every loss this time of year "two or three steps backwards" while every victory feels like only one forward.

If it's true, then Wednesday's 117-104 loss at Boston might measure double that much.

The Wolves opened a three-game trip that could tell their season's story with another loss or maybe even two by losing soundly to the Eastern Conference's second-best team and by losing key reserve Nemanja Bjelica to a second-quarter ankle injury.

Bjelica's injury as well as third-quarter foul trouble for both Rubio and starting big man Gorgui Dieng disrupted a Wolves team that was outscored 59-44 after halftime.

"There are things you can't control," Rubio said. "We couldn't control the tempo of the game for different reasons, and it was tough because we had a really good first half. The second half, we just didn't play right."

Afterward, Bjelica wore a protective boot on his left foot and left TD Garden on crutches. Wolves coach Tom Thibodeau said Bjelica will have a magnetic resonance imaging (MRI) test done on Thursday, but both his glum expression and Bjelica's, too, as he clattered into the good night didn't bode well.

The Wolves now trail Denver by four games for the Western Conference's eighth and final playoff spot and still must climb over both Portland (two games behind the Blazers) and Dallas (three back) with just 15 left.

"Every game is very important, us losing is a big loss," said Karl-Anthony Towns, whose streak of consecutive 20-point games ended at a franchise-best 21 games after he scored 17 Wednesday. "Us losing is a big loss. Every game is important. I can't stress that enough. Every game is putting us closer and closer or father and farther. We took a step back today. We have to regroup and get ready for Miami."

If the Nuggets go 7-8 the rest of the way, the Wolves would have to finish 11-4 to tie them.

Bjelica's injury wasn't the only one: Reserve guard Lance Stephenson had played just two minutes in the fourth quarter when he aggravated an ankle injury that caused him to miss three weeks last month.

By then, Thibodeau and the Wolves were left to improvise, both because Bjelica was out and because Rubio and Dieng were limited by foul trouble.

Leading by 10 points midway through the second quarter, the Wolves allowed Boston seven unanswered points just before halftime and then were outscored 27-17 in a decisive third quarter when the Celtics flexed their defense and big man Al Horford's versatility at both ends of the floor.

Trailing just 74-73 with less than five minutes left in the third quarter, the Celtics scored 19 of the next 24 points, primarily by reserves, just as the Wolves' bench had helped build a 46-36 lead before Bjelica left injured.

The Wolves trailed by a point when Rubio got his fourth foul midway through the third quarter. They trailed by three points when Dieng got his fourth two minutes later.

"But we let go," Thibodeau said. "We had too many mistakes to win on the road against this type of team."

His team never recovered and fell behind by as many as 19 points in the fourth quarter. Bjelica had four double-doubles in his past seven games before Wednesday.

"It's big," Rubio said about Bjelica's absence. "He has been giving us a lot of great minutes, and I hope he can continue playing. But we saw it tonight how our options went with him when he went down."

Thibodeau said his team must push on because there's no telling what might happen.

"Get ready for the next one," Thibodeau said. "There is a lot of head-to-head going on right now. You just get ready for the next one. I've seen a lot of stuff happen over the years."