Tim Thomas scored 25 points and Cassell and Ray Allen added 23 apiece for the Bucks, who won their fourth straight game.
After Thomas hit a pair of free throws with 3:08 left in the third quarter to give Milwaukee its biggest lead at 84-64, Indiana closed the period with an 11-1 run.
The Bucks extended their advantage to 97-81 on Allen's fourth 3-pointer with 5:57 left. Indiana went on a 13-0 spree that was capped by a short jumper by Jalen Rose with 2:15 remaining.
 Jermaine O'Neal writhes in pain after injuring his knee. Ron Hoskins NBAE/Getty Images |
But Jonathan Bender hit a pair from the line with 51 seconds left, and Rose made a 3-pointer with 24 seconds to go to get Indiana within 101-99.
Thomas sank a pair from the line before Rose drilled another 3-pointer with 13 seconds left to get the Pacers within 103-102.
After Allen made only 1-of-2 at the line, Rose was fouled in the lane, but he missed his first free throw. He intentionally missed the second free throw, but the rebound went to Cassell, who hit his pair to conclude the scoring.
"This was one that we had to have," Cassell said. "We've got to do a better job of putting teams away. We had them down real big. Then they started to hit some shots. I give them a lot of credit. It seems like we can't (hold) a lead. But again, they made some shots to get back in the game and I take my hat off to them."
"Our leadership is terrible right now," Milwaukee coach George Karl said. "Our stars, Sam and Ray, are just selfish. We had more assists in the first half than the second. For once, I would like to see more in the second half of the game. We seem to get more selfish late in the game."
Rose made a career-high four 3-pointers and scored 26 points to lead Indiana, which lost its second straight game.
Jeff Foster had 10 points and 13 rebounds, and Bender added 14 and eight. Jamaal Tinsley tallied 11 and 12 assists for his 13th double-double, tying him with Memphis' Pau Gasol for the most by a rookie.
Indiana's Reggie Miller added 24 points but was ejected with 9:57 left after picking up his second technical foul in five seconds. He had thrown Allen to the ground for the first technical, was benched by coach Isiah Thomas and was hit with the second one while yelling at the referees from the sideline.
"Everybody gets frustrated during the course of the game," Allen said. "whether it's something that a teammate does, or a call that a referee makes, a lot of times as players I think we let the referees control our situation. We can't let that happen. We have to play through and forget about it."
Indiana center Jermaine O'Neal was carried off the floor with 4:47 left in the second quarter after teammate Tinsley fell into him. O'Neal suffered a sprained left knee and did not return after registering seven points and eight rebounds in 17 minutes.
"I don't know what happened," O'Neal said. "I just remembered someone falling into my knee and pushing me backwards. It's real sore."
"He's a huge part of what we do and the way the league is, you take a monster off the team, you're not the same team," Thomas said.
The Pacers led by as much as 20-9 and took a 34-27 advantage into the second quarter. But behind Allen's 12 points in the period and Indiana's 4-of-16 shooting, Milwaukee took a 59-44 lead into halftime.
"I thought our second unit came in and was just terrible," said Thomas. "We've got pretty good players on that unit. We've got to get more out of that unit, and it's not at the offensive end, it's at the defensive end."
The teams play the second of their home-and-home series Wednesday in Milwaukee, but O'Neal will not make the trip.
"We've got to find a way to go up there tomorrow and get the job done," Rose said. "Even without Jermaine, we should have the firepower within to offset. We can't dwell on his absence. We've got to build on this."