In a classic plot twist to spice up the NBA playoffs, Harden and his Houston Rockets faded just enough in the final stretch of the regular season to drop to the No. 8 seed in the Western Conference, just as his old team locked up the top seed.
That set up a first-round clash between Harden and the Oklahoma City Thunder, the team that drafted him and where he spent his first three seasons in the league.
"I knew it was going to happen like this, for some reason," Harden said. "That's the beauty of it, that's what basketball is."
Harden, who couldn't agree to terms to extend his contract past this season in Oklahoma City, was dealt to Houston just prior to the regular season and led the Rockets to the postseason for the first time in four years.
Moving out of the sixth man role that he excelled in with the Thunder, Harden proved himself to be an All-Star while ranking fifth in the NBA in scoring this season.
"He's a good player. He had a great year, a regular-season All-Star. He has helped their team get to the playoffs with all of the work he has put in," Thunder coach Scott Brooks said. "They have some good players around him, too. Just like us, we're not a one- or two-man team. We're a good team and they're a good team. We're going to be focused on stopping all their players.
"It's definitely not going to be, `How are we going to stop James?' It's always about how are we going to stop the Houston Rockets from scoring on us."
Game 1 is Sunday night in Oklahoma City.
During his time with the Thunder, Harden built friendships with All-Stars Kevin Durant and Russell Westbrook, who were his neighbors in the locker room. But since the end of the regular season, when the Rockets dropped into the match-up, they haven't talked.
"It's all business now," Harden said. "Those guys are competing for a championship, so it's all business."
Durant had a similar sentiment.
"That was so long ago. So much stuff has happened since then. We've got Kevin Martin, guys have gotten better and James has moved on," he said. "It's the Thunder versus the Rockets. That's all we're focused on."
Considering the history, Harden figures to be a central figure in the series. He scored a career-high 46 points in Houston's only win in three games against the Thunder this season. In his only return to Oklahoma City after the trade, Harden made only three of his 16 shots and got six of them blocked.
"I think a lot of it just has to do with pride. We're going to lock in. Obviously, with the whole James thing, he probably wants to have a good game and we don't want him to have a good game," Thunder center Kendrick Perkins said. "That's just how it is."
The series will feature two of the NBA's top three teams in scoring, with Houston averaging 106 points per game and Oklahoma City right behind at 105.7. A big part of the Thunder's preparations has been getting ready to slow down the transition game of the Rockets, who like to run even after an opponent's made basket.
"Your first three steps in transition have to be full speed, because those are the most important steps in getting back on defense," Brooks said. "You have to have a mindset to do it every time.
"There's no celebrations, there's no frustrations with a call that didn't go your way because while you're doing it, they're scoring at the other end."
That's a particularly relevant message since the Thunder's frequent complaints to officials have put them among the league leaders in technical fouls. Westbrook tied for the most in the league with 15, and Durant and Perkins had 12 apiece.
"It's going to be really important for us to run back on defense and get set and really stick to our principles," said Thabo Sefolosha, who figures to be guarding Harden most of the time.
The Rockets bring in a roster that is youthful like the Thunder but without as much postseason experience. Harden and ex-Bulls center Omer Asik are the playoff veterans compared to first-timers Jeremy Lin and Chandler Parsons.
"When you're a kid and you're playing a guy 1-on-1 in the park, you've got to find one way to beat him. You don't have to worry about anybody else. You've got to beat him if you want to win," coach Kevin McHale said. "What we've got to do is find a way to beat Oklahoma City and that's our main focus."
Each of the past three seasons, with Harden on the team, the Thunder progressed further than the previous year -- making the playoffs in 2009 but getting knocked out in the first round, then losing in the West finals before last year's NBA Finals defeat against Miami.
And this time, they'll try to keep moving on without Harden.
"It's fun," Westbrook said. "He has his team. He wants to win just as much as we want to win, so it should be fun and interesting."
AP Sports Writer Chris Duncan in Houston contributed to this report.