Fourth-seeded Tommy Haas also advanced, beating Nicholas Mahut of France 7-6 (4), 6-3.
Del Potro cruised through the opening set, struggled in the second, and broke Sela a sixth time for the match.
The 19-year-old Argentine, ranked a career-high No. 19 in the world, has not lost in six weeks. Del Potro has won all three tournaments he's entered. He picked up his first career title in Stuttgart, Germany, and kept the streak going with wins in the Austrian Open and Los Angeles last weekend.
It's the first time any ATP player has picked up his first three career titles in three straight tournaments.
Del Potro will meet last year's runner-up, John Isner, in the quarterfinals. Isner defeated Donald Young 6-4, 7-6 (4) in an all-American affair.
Young was overpowered by the 6-foot-9 (2.06-meter) Isner's serve. Isner had 17 aces in the match, and Young was visibly frustrated at the end of the tiebreaker. After hitting a long unforced error to go down 5-4 in the tiebreaker, Young threw his racket to the ground. After failing to return Isner's next serve, Young kicked the racket before going to his bag for a new one.
The new racket didn't help Young, who returned Isner's final serve wide to send Isner to the next round.
In contrast to del Potro, who cruised early before running into trouble, Haas had his tough times early in the match. Serving with a 5-3 lead in the first set, Haas double-faulted three times to give Mahut a break.
"That drove me a little bit crazy,'' Haas said. "Just to not make him play, especially when I was serving for that first set.''
Those were just the most damaging of seven double faults for Haas in the opening set. The German said his shoulder was a little bit tight, and after he missed on a few serves he started to overthink the motion.
Haas settled in after the first-set tiebreaker, winning the final four games of the second set to end the match. He had no double-faults in the second set.
Mahut had beaten Haas in the pair's two previous meetings, a mark Haas had specifically pointed out after his first-round win.
"I was really looking forward to the match,'' Haas said. "When I finally broke him it felt good.''
Haas will face Alejandro Falla after the Colombian prevailed against Florent Serra of France 7-6 (2), 7-6 (11) in 2 hours, 26 minutes.
Falla, who defeated fifth-seeded Mardy Fish in the first round, said his right quad was cramping when he was down 6-5 with Serra serving in the second set. He battled through it to force the tiebreaker and throughout the long rallies of the 24-point final game.
"Everything happened in the tiebreak,'' Falla said. "Set point for him, match point for me. It went so long - there were long rallies and some amazing balls.''
Falla was down 6-5 in both sets and was also down 6-5 in the final tiebreaker. The match ended when Serra hit a ball into the net during a rally.
"It was a very good sensation,'' said Falla, into his first quarterfinals since October.
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