Stephen A. Smith couldn't help but notice James Harden was very tired after playing 43 minutes, and is not surprised he got blocked at the end of overtime. (1:11)

SAN ANTONIO -- The basketball rolled up the AT&T Center court at roughly the pace of molasses dripping out of the jar on a cold winter day. James Harden slowly strolled behind with the clock frozen at 56.5 seconds remaining in overtime, finally bending over to pick up the ball just before crossing the half-court line.

Harden needed every precious second of rest he could steal down the stretch of a grueling Game 5. Ultimately, the engine of the Houston Rockets simply didn’t have enough fuel left in the tank to finish strong.

Even with fellow MVP candidate Kawhi Leonard helplessly watching from the San Antonio Spurs’ bench, sidelined by a sore ankle, Harden fizzled at the end of a frequently spectacular individual performance. He posted a 33-10-10 triple-double Tuesday night, but in overtime his sole contribution to that phenomenal line was just one assist.

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Harden committed three turnovers in overtime, twice getting the ball poked away from behind by feisty, fresh-legged Jonathon Simmons. He missed three shots, all 3-pointers. He came up short on the first two overtime misses, a telltale sign of heavy legs after playing 38 minutes in regulation and every second after that. Harden’s last attempt was cupped from behind by 39-year-old Manu Ginobili just before the buzzer sounded, sealing the 110-107 loss that put the Rockets on the brink of elimination.

“I’m all right. Just missed shots,” Harden said, refusing to use fatigue as an excuse for his failure to finish strong. “Missed shots and just didn’t make enough plays to win. Obviously, other players stepped up and made big shots, and that was the game.”

Houston coach Mike D’Antoni acknowledged that his team, down to a seven-man rotation after reserve center Nene suffered a season-ending torn left adductor in Game 4, got tired down the stretch. D’Antoni said as much in his postgame news conference and with his decision not to practice Wednesday, a rarity for the Rockets.

D’Antoni avoided a question about Harden’s fatigue, mentioning that players from both teams were clearly tired, but there’s no denying the Rockets require more from Harden than ever before.

Harden’s historically big offensive burden is nothing new. He led the league in assists and ranked second in scoring, accounting for 56.2 points per game, more than anyone in NBA history other than Tiny Archibald in 1971-72.

However, Houston could often hide Harden on defense, the luxury of playing with a pair of defensive stoppers in Trevor Ariza and Patrick Beverley. He could get some rest at that end of the floor. But that’s really not the case now that Nene’s absence has thrown a wrench in the Rockets’ rotation.

Harden was able to find success in the first half driving to the basket. But Harden was defended by Simmons on two drives after halftime. Both times, he turned the ball over. ESPN Stats & Info

D’Antoni has decided to give all the backup center minutes to Ryan Anderson. As a result, Anderson came off the bench for the first time all season in Game 5, replaced by Eric Gordon as the Rockets opted to go with a three-guard look.

That created a defensive matchup conundrum. Ariza absolutely has to be the primary defender on Leonard. Beverley, for all the pit bull qualities packed in his 6-foot-1, 185-pound frame, is simply too small to guard proven big scorers such as LaMarcus Aldridge and Pau Gasol. That means Harden has to accept that rugged responsibility.

Harden, whose defensive lapses inspired viral YouTube videos as recently as last season, rose to the challenge. He actually had a heck of a defensive performance, at least until Danny Green blew by a gassed Harden for an and-1 layup with 30.1 seconds remaining to give the Spurs the lead for good.

Harden was the primary defender on a team-high 20 possessions, according to ESPN Stats and Information tracking, and the Spurs got only seven buckets out of those trips. Aldridge and Leonard, whom Harden had to guard several times after switches, were a combined 0-for-8 against him. The 6-foot-5, 220-pound Harden fought hard and used leverage and strength to consistently push Aldridge and Gasol off their sweet spots, as evidenced by the Spurs’ bigs going just 1-for-3 on post-ups against Harden despite a significant height advantage.

“Just try to be aggressive, do the best I can and help my team,” Harden said, describing his defensive strategy against the skilled big men.

It certainly seemed to take a toll late in the game. Harden’s numbers in the clutch -- defined as the last five minutes of regulation and overtime when the score is within five points -- were four points on 1-of-6 shooting, one assist and four turnovers. All of those misses were 3s, as Harden kept settling for long jumpers instead of attacking off the dribble.

“I just didn’t have a rhythm,” Harden said. “A couple of good looks I had, I missed them. But it comes with it. I’ll take those same shots and just continue to be aggressive.”

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It’s hard enough for Harden to have enough in the tank for crunch time when he doesn’t have to bang with bigs for most of the night. The biggest blemish on Harden’s MVP candidacy was his relatively poor clutch performance in the regular season, particularly when compared with Oklahoma City’s Russell Westbrook and Leonard.

The Rockets were minus-27 in Harden’s 134 clutch minutes this season. His shooting percentages -- 35.3 percent from the floor, 27.3 percent from 3-point range and 75.8 percent from the line -- were down significantly from his norms across the board. He had as many turnovers (20) as assists.

On Tuesday night, the Rockets needed Harden to buck those trends. He just didn’t seem to have the legs down the stretch to do it, and it didn’t help that Houston’s late rebounding struggles halted its running game, forcing Harden to attempt to create scoring opportunities in grind-it-out half-court sets against the NBA’s stingiest defensive squad.

“We’ve got to find the energy to get ready for the next game in Houston and try again,” D’Antoni said. “We played well enough to win. We just didn’t finish the job.”