Kevin Durant matched his season high with 37 points and the Thunder beat Houston 120-98 on Wednesday night, after the Rockets made a stop in Minnesota earlier in the day to attend the funeral of coach Kevin McHale's daughter.
Harden scored 17 points but was limited to 3-for-16 shooting. He had six shots blocked by the Thunder.
After a draining 24 hours, he was ready to put it behind him.
"It felt good just to be competing against those guys and finally get this over with, to play here and get it over with," Harden said. "Now, I can continue on with the season."
Harden missed his first nine shots, and by the time he made one, the Rockets were down by double digits in the second half. They never got closer than 10 after that.
Harden, the NBA's Sixth Man of the Year as Oklahoma City made it to the NBA Finals last season, was unable to agree on a contract extension with the Thunder and was traded just before the season started.
Harden said before the game that he thought there was a "very slight chance" that he'd be traded. He has complained that general manager Sam Presti gave him only one hour to mull over Oklahoma City's final offer before the trade.
"One minute, I was at dinner with my family. The next minute, I'm headed to Houston," Harden said. "It happened pretty quick."
Harden then agreed to a maximum contract worth $80 million with Houston -- something Oklahoma City wasn't willing to offer; there would have been severe salary-cap ramifications if it had.
Harden said he felt "relaxed" and not pressured by the circumstances, although it didn't show in his game. Only a meaningless 3-pointer in the final 3 minutes prevented him from his worst shooting percentage yet with Houston.
"I just couldn't finish the ball around the basket," Harden said. "I had a couple of good looks. I think the other guys feel the same way."
Harden was at the center of a heated first-half incident that got Thunder backup center Hasheem Thabeet temporarily ejected. Thabeet and Harden exchanged words after Thabeet blocked two consecutive shots by Harden. Thabeet then bumped into referee Marc Davis and pushed him away, resulting in an ejection. But Davis went to instant replay and downgraded the punishment to a single technical foul.
Fans gave Thabeet a standing ovation when he returned to the court, and booed lustily as Harden made his free throw. It was Harden's first point of the game and one of only two in the first half. Harden missed all eight of his shots from the field as Houston fell behind 57-45, never really threatening after that.
"It's crazy," said Durant, who admitted he couldn't sleep overnight or when he tried to take a nap Wednesday. "Seeing him before the game and in chapel just in a different uniform is a little different. We've moved on past it, man. We're happy to see him, glad he's doing well out there in Houston but we wanted this win bad.
"For all those days in practice where him, Daequan (Cook) and Eric Maynor beat the first group, I wanted this win real bad."
The Rockets had flown to Minnesota after blowing out Toronto on Tuesday night, arriving at the team hotel between 1:30 and 2 a.m. They were back up by 8 for a team brunch and a scouting report in suits and ties before they went to the funeral.
Acting coach Kelvin Sampson said McHale and his wife, Lynn, were arranging candles near some photos of Sasha and didn't immediately see the team walk in.
"We didn't know what to do or say, so we just waited for them to get finished, then they turn around and at the same time they looked at us," Sampson said. "Really, really, really emotional."
McHale hugged everyone in Houston's traveling party and shared a few words with each person. He took a leave of absence from the team on Nov. 10. Sasha died Saturday at age 23 of complications from lupus.
"Just to see our faces, I think, kind of gave him some kind of joy. Just to show him that we were there, our whole entire organization was there just to support him," Harden said. "No matter if it was for 5 minutes or 30 minutes, he just wanted to see our faces. I'm glad we got that opportunity to go out there and share that moment with him."
The team then flew to Oklahoma City, arriving at the arena less than 5 hours before game time. Sampson said about half of his players were in the locker room with towels over their heads, trying to squeeze in a nap during the afternoon.
Patrick Patterson scored 27 points and Omer Asik had 17 points and 12 rebounds to lead the way for the Rockets. Daequan Cook, also involved in the Harden trade, scored 18 points while starting in place of injured Rockets forward Chandler Parsons (shoulder).
Before the game, the Thunder flashed a welcome back message to the players who were traded away and Harden got a warm ovation during starting lineups. Harden and Cook both greeted coach Scott Brooks and others on the Thunder bench just before tipoff.
Harden missed his first four shots -- getting a jumper swatted from behind and out of bounds by Westbrook, and a fast-break layup blocked as Ibaka followed him to the basket -- and committed two early turnovers. Cook also missed his first three shots, but then hit a jumper and a 3-pointer for a 19-14 Houston lead.
Oklahoma City took the lead for good with an 18-4 run, including the first nine points of the second quarter, and went up 36-25 before Thabeet and Harden had their run-in.
The lead grew to 49-33 after Harden's foul allowed Durant to convert a four-point play.
"Every day at practice, we had a war. I knew what each and every one of those guys do well and what they don't do well and vice-versa," Harden said. "I couldn't guard all five of them."
Sampson formerly coached at Oklahoma for 12 seasons. "The circumstances that I took over this position with, I just don't feel comfortable talking about me. I talk to Kevin every day. I talked to him the day his daughter died. I'm really, really close to Kevin and I'm holding the fort down until he comes back." ... Parsons hurt his right shoulder late in Houston's win against Toronto on Tuesday night. "I don't think it's a joint. I think it's more soft tissue, but he can't get his elbow past 45 degrees," Sampson said