BOSTON -- Brandon Jennings had another big opening night for the Milwaukee Bucks, just as he did in his first game as a pro.
He enjoyed Friday night's debut a lot more.
"We lost that game" in 2009, he said. "So I was glad to take this one."
The Bucks took it to the Celtics from the start -- outhustling them and playing better offense and defense -- and ruined Boston's home opener with a 99-88 win that broke Milwaukee's streak of five consecutive opening-game losses.
Jennings had 21 points, 13 assists and six steals. In his first NBA game, he had 17 points, nine rebounds and nine assists but lost 99-86 at the Philadelphia 76ers.
On Friday, the Bucks didn't trail after the first 6 minutes and led by at least 11 points throughout the second half.
Boston had cut a 46-30 halftime deficit to 48-35. Milwaukee scored the next six points and led 76-58 going into the fourth quarter.
"In the third, when they started to get after it, started to bump us, we responded really well," Bucks coach Scott Skiles said. "We had a lot of energy. Guys were doing their jobs out there."
The same can't be said for the Celtics.
They allowed the second-fewest points in the NBA last season, but struggled defensively for the second consecutive game. They lost 120-107 to the Miami Heat on Tuesday night, matching the most points they allowed in any game last season.
"We have a lot of new people, a lot of guys trying to get adjusted," said Jason Terry, who signed in the offseason as a free agent from the Dallas Mavericks. "It's going to take a while, but to get outworked is definitely unacceptable."
Boston was led by Kevin Garnett with 15 points and Rajon Rondo had 14 points and 11 assists. The Celtics lost their first three games last season but reached the Eastern Conference finals where they lost in seven games to the Heat.
"It starts and ends with our defense," Rondo said. "I'm the point guard. I'm the first line of defense and initiate the offense. I've got to be better."
The biggest cheers of the night went to David Ortiz, the Boston Red Sox designated hitter seated in the front row at midcourt.
A baseball official with knowledge of the negotiations said the team and Ortiz had agreed to a two-year, $26 million deal. Several fans shouted "congratulations" to Ortiz as he walked to his seat early in the third quarter. A loud cheer went up when he was shown on the video scoreboard, then he raised his left arm straight up to acknowledge the crowd.
Later in the quarter, the fans booed the Celtics when Monta Ellis hit a layup after a steal by Jennings, giving the Bucks a 66-46 lead with 4:10 left in the period.
Tobias Harris scored 18 points for Milwaukee and Ellis had 14.
The Bucks led 94-72, matching their biggest lead, on a basket by Jennings with 3:45 to go in the game before the Celtics whittled the final margin to 11 points.
The Celtics have just six players who saw action with the team last season and are struggling defensively after holding opponents to the lowest field goal percentage in the league, 41.9 percent. Offensively, the Celtics could do little inside.
"We locked down that paint pretty good," said Larry Sanders, who had 10 points and seven rebounds for the Bucks. "We were all dependent on our teammates."
The Celtics allowed the Heat to shoot 54.4 percent in the opener and the Bucks to make 46.5 percent. In their final regular season game last season, the Celtics beat the Bucks 87-74.
"We missed the playoffs two years in a row, so it started from tonight," Jennings said. "Whether I shoot bad or not, just as long as they know I gave it my all."
Milwaukee took control after Paul Pierce gave Boston its last lead, 10-8, with two free throws with 6:34 left in the first quarter.
Jennings followed with a layup, Ersan Ilyasova made a short jumper and Ellis dunked on a fast break for a 16-10 lead. It was 25-18 after one quarter before the Bucks held the Celtics to 12 points in the second quarter.
Boston improved its shooting in the third quarter, hitting 56.3 percent, but committed seven turnovers that led to 10 points.
"I don't like our urgency yet," Celtics coach Doc Rivers said. "When you watch us play, I don't like how we're approaching the games. And until we [improve] that, we're going to struggle."