A 14-0 run early in the fourth quarter gave the Blazers a narrow lead, which they held until T.J. Ford's jumper put the Pacers back up 99-97.
The teams wrestled until Roy's pull-up jumper put Portland ahead 103-101 with 1:22 to go. Roy added a pair of free throws with 40.5 seconds left.
But Daniels made two free throws of his own before a dramatic steal and dunk with 11 seconds left to tie it at 105.
Ford was called for tripping Roy on the other end, and Portland's All-Star guard put the Blazers ahead. After a timeout, former Blazers guard Jarrett Jack missed a 3-point attempt from out front at the buzzer.
Jack said the call was fair.
"I thought it was a tough call at first but we came back and looked at it and thought the ref had a better look at it than we did," he said. "We have no gripes of complaints."
The Pacers, coming off a 117-109 victory over Sacramento on Tuesday night, remained without All-Star forward Danny Granger, the team's top scorer, who is recovering from a torn tendon in his right foot.
The Blazers remained without Greg Oden, who has missed eight games because of a bone chip in his left knee. The Blazers said the injury will be reevaluated in about a week.
The 7-foot center was hurt in a collision during a game at Golden State before the All-Star break. The top pick in the 2007 draft sat out last season after microfracture surgery on his right knee and he missed six games early this season with a foot injury.
Indiana took a 35-24 lead in the first half after Daniels' dunk. Portland pulled within 38-37 on Travis Outlaw's layup off a well-timed pass from Rudy Fernandez.
The Blazers could not get closer and the Pacers led 59-52 at the half.
Indiana stretched the lead to 79-65, seemingly unaffected by having played the night before.
Portland narrowed it to 88-86 in the fourth quarter with Fernandez's 3-pointer from the corner. Steve Blake added another 3-pointer to give the Blazers an 89-88 lead.
Another Blake 3 made it 92-88, capping a 14-0 run.
The Blazers moved to within a half game of the Northwest Division-leading Nuggets, setting up a battle for first place in the division race when Portland visits Denver on Thursday night.
"It's going to be nice. I just wish we didn't have to get them on a back-to-back but we'll be ready," said Travis Outlaw, who had 21 points off the bench.
Indiana's last loss in the series was a 97-95 overtime defeat Dec. 3, 2003, at the Rose Garden. ... Before the game, the Blazers helped raise money to help pay for the care of Nathan Vredevelt, a 16-year-old with Down syndrome, who was struck by a car and critically injured after wandering away from Sunday night's game at the Rose Garden. The team said it would match donations up to $10,000. ... Boxer Roy Jones Jr. attended the game. Jones is promoting a fight this weekend at an Oregon casino. ... Pacers president Larry Bird also was at the game.