The top-seeded player, Shelton enjoyed a bye through the first round of ATP 250 tournament which he has chosen to start his season in each of his last four years.
With his coach and father Brian Shelton and his partner, US women's soccer team star Trinity Rodman courtside, Shelton saved a set point in the first set to beat 68th-ranked Argentina player in one hour, 42 minutes.
Shelton had 12 aces and won 78 per cent of first-serve points but his game showed signs of recent inactivity.
"I feel great, knocked off a little bit of rust but just feel great to be back playing, back competing," the world No.8 said.
"I think it's great when you get to play a competitive match, feel the tension at certain points of the match and then obviously get a win and give yourself the opportunity to play again."
Shelton faced a break point in his first service game as he tried to get into his rhythm, backing up his first serve by attacking short returns. He found Comesana's serve hard to crack at first. The Argentine had a set point at 5-4 but with Shelton at the net and the back court open, he overhit his backhand down the line.
It was his last chance. Shelton held then broke Comesana for 6-5 and held to take the set in one hour, 29 minutes. He then broke Comesana again in the first game of the second set and carried the break to clinch the match.
The ATP Auckland stop is a tuneup event for the Australian Open which starts Sunday in Melbourne.
Second-seeded Casper Ruud bowed out in the second round to unseeded Hungarian Fabian Marozsan 6-4 6-4. Marozsan ousted defending champion Gael Monfils in the first round.
The 68-ranked Marozsan broke Ruud's serve in the opening game and offered only one break point chance before taking out the first set in 40 minutes.
Ruud lifted his serving game in the second set but Marazsan broke again in the ninth game and held serve to take the match.
"I had a great serve today and I tried to push my game, tried to be aggressive, tried to believe in myself and everything just happened today," Marozsan said. "It was a good day for me and hopefully I can keep going."
Fifth-seeded Briton Cameron Norrie also fell in the second round, beaten 4-6 6-3 7-6 (7-4) by Frenchman Giovanni Mpetshi Perricard.
Alejandro Tabilo, the 2024 Auckland champion, beat fourth-seeded Luciano Darderi 1-6 7-5 6-3.
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