MELBOURNE: John Isner could have a slight scheduling conflict when he plays his fourth-round match at the Australian Open on Monday — it may coincide with the NFC Championship game being played in the US between the Arizona Cardinals and his beloved Carolina Panthers.

"Maybe (I'll) go to the tournament desk and ask for a late start," Isner, a North Carolina native, said. He added that tournament director Craig Tiley would "probably just laugh at me."

But Isner said if he misses the game, so be it. What's more important is he's back in the second week at Melbourne Park for the first time in six years after defeating 18th-seeded Feliciano Lopez 6-7 (8), 7-6 (5), 6-2, 6-4 on Saturday.

"It's been a little while since I've been in the round of 16 at this tournament," he said. "It feels great. I'm very relieved to get through, want to keep on going."

The 6-foot-10 (2.08 meter) Isner has one of the biggest serves on tour — he had 44 aces against Lopez to increase his tournament-leading total to 101 through three rounds — but this hasn't exactly translated to success at the Grand Slams, where he was 5-12 in third-round matches before Saturday's win. He's only reached the quarterfinals once, at the 2011 US Open.

Since hiring former ATP player Justin Gimelstob as his coach at the end of 2014, however, Isner's game is on the upswing again. His ranking has climbed from just outside the top 20 to No. 11, and he's now reached the round of 16 at back-to-back majors.

Isner exacted some revenge against Lopez as well. The Spaniard had beaten him in five sets at the Australian Open in 2012 — in the same round, and on the same court in Hisense Arena.

"I feel like I've gotten just better in general as a tennis player," he said. "Not so much things that I'm doing very different. I'm still working hard, taking care of myself. But it's a bit of a mindset, I would say. ... Mindset and a belief."

That belief was evident when Isner dropped the first-set tiebreaker to Lopez after saving four set points and holding a set point of his own. His racket got a pummeling during the changeover, but he regained his composure and pulled out a tight second set before clinching the match.

"The second set could have gone either way," he said. "That was definitely the turning point. I freed up and started playing so much better after that."

Like many men's players, the 30-year-old Isner is playing some of his best tennis in the later stages of his career. He was one of 13 men over 30 to reach the third round at the Australian Open — the most since 1977. After beating one fellow 30-something in Lopez, he faces another on Monday — 33-year-old David Ferrer.

American Steve Johnson, who lost to Ferrer on Saturday, said Isner's commitment to the game hasn't diminished, nor has his lightning serve. In fact, he could be more dangerous than ever.

"The sense of urgency is definitely higher because he probably doesn't have that many more years left in him," Johnson said. "And he realizes that."