Portland's laundry list of injuries includes center and Indianapolis native Greg Oden (left knee), guard Rudy Fernandez (sciatic pain) and forward Travis Outlaw (left foot). McMillan, who didn't travel, had surgery on his right Achilles' tendon after injuring it during a team practice Dec. 4.
"That's just the type of guy Nate is," said Roy, who added seven rebounds and five assists. "We were down a lot of bodies that day, he wants to get out there and play. It's just too bad his body couldn't hold up. It says a lot, though. He cares about this team."
Trail Blazers assistant Dean Demopoulos, who's assuming head coaching duties while McMillan recovers, plans to teach from the sideline.
"Even when I was young enough, I wasn't good enough," Demopoulos joked. "I'm 10 or 11 years older than Nate. I'd blow both Achilles' out."
Demopoulos and the Trail Blazers didn't need a full complement of players to beat the struggling Pacers. LaMarcus Aldridge had 20 points and eight rebounds, and Andre Miller scored 15 for Portland (14-9), which snapped a four-game road losing streak.
"When you talk about team wins, this is the essence of team," Demopoulos said. "Everyone stepped up, held hands and collectively got it done."
The Pacers, on the other hand, continued their downward spiral. Dahntay Jones had 19 points and rookie Tyler Hansbrough added 13 points and 11 rebounds for Indiana (6-13), losers of six straight.
The Pacers played without injured All-Star Danny Granger, who is expected to miss at least four weeks with a torn right plantar fascia. The team's leading scorer won't require surgery.
"It's back to the drawing board," Jones said. "Losing is not fun."
The Pacers, who trailed by 11 in the first half, tied the score at 83 on Luther Head's jumper with 8 minutes left in the fourth quarter. Portland used an 8-2 run, capped by Miller's layup, to take a 100-91 lead. Roy had consecutive baskets to spark the rally.
"I could almost fall asleep when he's got the ball," Demopoulos said of Roy. "That's how comfortable I feel with him. He always comes through."
The Trail Blazers shot nearly 53 percent in the first quarter and opened their biggest lead, 26-15, on Roy's 3-pointer. Indiana got within four late in the second, but Aldridge's two free throws pushed the lead back to 52-45 at the break.
"We didn't play consistent basketball," Pacers coach Jim O'Brien said. "We can't play two and a half quarters of good basketball and one and a half quarters of sub-par basketball."
Aldridge was impressed with the Trail Blazers' ability to play short-handed.
"I don't see it as overly tough," he said. "If we come out and play hard, I feel like we have enough guys to win now. We have to live in the moment."
Oden could miss the rest of the season after having surgery on his left knee. ... McMillan is not expected to coach the team's next two games at Cleveland and Milwaukee. ... The Pacers have lost 10 of 11 after winning five straight.