The Italian big man played for the first time since missing 26 games with an elbow injury, and checked in to a mixed reception of boos and cheers in Toronto's 99-95 loss to the Boston Celtics.
Numerous fans stood and gave two thumbs-down signs.
"I'm disappointed because this young man has done nothing to deserve that," Raptors coach Casey said after the game. "He's been hurt. Fans have a right to boo, cheer. . . Boo me. Whoever they want to boo. But I don't think Andrea deserves that.
"Young man's coming back from a serious injury. But he was a pro about it, came in and played, and gave us everything we needed."
Kevin Garnett poured in a game-high 27 points and grabbed 10 rebounds to lead the Celtics to their sixth consecutive victory.
Rudy Gay had 25 points and 12 boards to top Toronto (17-32).
Bargnani had a decent outing, scoring 13 points on 5-for-10 shooting in 24 minutes.
He seemed unfazed by the boos.
"(I had) no reaction. I tried to focus on the game," Bargnani said. "I heard some cheers, some boos, I tried to be aggressive and tried to help my team.
"It's not my role to say if (the booing) is fair or unfair. I've just got to go in and try to contribute to the team."
Kyle Lowry added 17 points and eight assists, and Amir Johnson finished with 16 points and 12 rebounds.
Neither team dominated what was a pedestrian affair until midway through the third quarter when Lowry, Gay and Bargnani worked — at least for a stretch — like a well-oiled machine. In one four-second span in the final minute of the frame, Gay drained a three-pointer, stole the ball off Jason Terry and found a sprinting DeRozan who finished with a layup and a free throw after being fouled on the play.
The Raptors led 79-69 with one quarter left.
The Celtics fought back with a 21-6 run in the fourth, Garnett's basket with four minutes left putting Boston up 90-85. Gay cut Boston's lead to three points with 43 seconds left, but a Jeff Green free throw put Boston up by four with 18 seconds left — and the game virtually out of reach.
Courtney Lee added 15 for the Celtics (25-23), who are missing all-star guard Rajon Rondo (season-ending anterior cruciate ligament tear). Paul Pierce had 12 points to go with 11 rebounds.
"I thought we came out tip-toeing into the game where I thought they came out the hungrier team," Casey said. "I thought we got that mojo back after halftime but we didn't start the game with the same type of excitement and enthusiasm and the fight that we have to step on the floor with and that was disappointing."
Leandro Barbosa, playing his first game back in Toronto since the Raptors traded him last March, scored 12 of his 14 points in the fourth quarter.
Bargnani, the No. 1 pick in the 2006 draft, hadn't played since tearing ligaments in his right elbow and spraining his right wrist Dec. 10 at Portland — the Raptors went 13-13 in his absence.
Casey warned that Bargnani would have plenty of rust, but he had some decent moments Wednesday, altering shots with his length, and scoring on layups and jumpers. Midway through the third quarter he went hard to the hoop for a dunk that brought the Air Canada Centre crowd of 17,163 to its feet.
"It feels great," Bargnani said. "I stayed out eight weeks, wasn't able to shoot the ball for seven weeks. I've definitely got to get back in rhythm, get back in shape."
"Being out for so many weeks, I've got to play harder on the defensive end because on the offence, I'm out of the plays of course," he added. "I've got to get back in the offensive flow."
Trade speculation — the NBA trade deadline is Feb. 21 — has swirled around the seven-footer, who hasn't played with nearly the same intensity as he did last season before a calf injured derailed that campaign.
"Just getting that extra step out of him, like what happened early last year, is the key," Casey said. "Whatever I have to do, kick him in the butt, be his friend, pat him on the back, hit him in the head. . . whatever it takes to get him to that level is going to be huge for our team going forward."
Bargnani has been an enigma since he arrived in Toronto, a talented player who is frustratingly lacklustre in his play at times.
"I'm not a psychologist," Casey said. "He's a quiet man, and I think people mistake that for not caring. I do think he cares, I do know he cares, that's the part of Andrea's personality that no one has ever been able to grasp upon.
"But there's a lot going on upstairs, he's a smart guy, he does care, he's very conscientious of where he stands with the team in the league."
Gay said his new teammate is the kind of player who can't be classified as a centre, power forward or forward.
"He's a basketball player and a great basketball player," Gay said of Bargnani. "For being out as long as he was, he played great today."
Gay led the way with eight points in a sleepy first quarter that saw the Raptors lead 23-20 going into the second.
Bargnani scored 11 in the second, his turnaround jumper giving Toronto a three-point lead — its biggest of the quarter. The Celtics went up by six on a 14-5 run and led 50-45 at halftime.
The Raptors outscored their visitors 34-19 in the third, DeRozan's three-point play putting Toronto up 79-69 heading into the fourth.
NOTES: Toronto was missing Landry Fields for the second straight game (back spasms). . . The Raptors are at Indiana on Friday then return home for games against New Orleans and Denver.