The San Antonio Spurs have won 18 consecutive games against the Boston Celtics, but the Spurs' effort in their last outing has coach Gregg Popovichconcerned.

San Antonio (46-19) hopes to avoid back-to-back losses against two of the league's worst teams as it hosts the Celtics on Saturday.

The Spurs lost 101-90 to the Milwaukee Bucks on Thursday, ending their 13-game winning streak. Brent Barry lead the team with 20 points while Tim Duncan - the team's leading scorer at 20 points per game - scored just 13.

Manu Ginobili had 12 points and Tony Parker 15 - both below their season averages of 17.1 and 18.4, respectively.

"That's not going to happen very often," Popovich said. "They're human beings, it can happen. But I'm more concerned with the lack of aggressiveness on both ends of the court."

Parker played just 6:14 in the fourth quarter, and while he wouldn't confirm it, Popovich hinted he was irritated with his point guard's defensive effort.

Parker himself said he struggled but would rebound against the Celtics.

"I didn't play well at all," Parker said. "I'll try to do better Saturday against Boston."

The 101 points allowed to the Bucks, who have the third-fewest wins in the NBA, were the most allowed by the Spurs since giving up 106 to Orlando on Feb. 9. It was just the 10th time San Antonio, which allows a league-best 89.7 points per game, has allowed 100-plus points this season.

Popovich said Thursday wasn't the only time he was disappointed, also pointing to San Antonio's 93-84 win over the Los Angeles Clippers on Tuesday as another poor performance.

"Eventually, you're going to have an off night, but that doesn't mean that you like it, or accept it, or you just kiss it off," Popovich said. "To have that poor of a mental focus or mental attitude two games in a row is disappointing."

Popovich and the Spurs hope to rebound against the Celtics (19-46) - whom they haven't lost to since Jan. 8, 1997, and a team they haven't lost to at home since Feb. 14, 1990 - a span of 16 games. Duncan has never lost to the Celtics since being drafted first overall by the Spurs in 1997, averaging 22.3 points and 11.2 rebounds in 17 victories.

Boston (19-46) is coming off a 106-101 defeat to Dallas Mavericks on Friday. The Celtics, who are trying to avoid being the last NBA team to 20 wins, blew a 10-point halftime lead after making 15 of their first 24 shots. After Dallas used a 16-9 run in the fourth quarter to take the lead, the Celtics rallied within one point with 1:03 left, but the Mavericks finished the game on a 6-2 run.

"It was a great effort," Celtics coach Doc Rivers said. "That's as close to the playoffs as we're going to get. We had a couple of possessions our young guys need to learn from."

Paul Pierce had 29 points, but was plagued by early foul trouble that held him to just seven minutes in the first quarter. Gerald Green added a career-high 25 and Al Jefferson contributed 20 and 10 rebounds.

Boston had won six of its previous nine. Memphis, with 16 victories, is the only other team yet to reach 20.

"At his point, we have nothing to lose," Pierce said. "We're out of the playoff race and we're just playing for pride."

San Antonio won the first meeting, 93-89 on Jan. 22, as Duncan had 21 points, nine rebounds, five assists and four blocks for the Spurs, while Delonte West scored 27 for the Celtics.

Copyright 2006 by STATS LLC and Associated Press. Any commercial use or distribution without the express written consent of STATS LLC and Associated Press is strictly prohibited