Mark said it was "cool" to "get back out there again" and to feel the high "energy" in the ballroom.
Mark and his celebrity partner, TikTok and The D'Amelio Show star Charli D'Amelio, topped the night by placing first on the Dancing with the Stars leaderboard with a score of 32 out of 40 possible points.
Charli and the touring musician danced the cha cha, and the judges gushed about how Charli showed rhythm and musicality.
"It's great to be in the top spot. We weren't anticipating that," Mark shared.
"The only thing we wanted to do was work super hard [and] maximize our rehearsal time and just do the best that we possibly could. And we had a good night tonight. So I'm proud of [Charli]."
Dancing with the Stars judge Derek Hough, Mark's longtime good friend, complimented Charli on her "attack" and the pair's "precision" throughout the routine on Monday night's show.
Derek also gushed about how it was awesome to be on the reality dancing competition with Mark again.
"You know, Derek and I have been friends since we were like 10. We've lived together, we went to school together every day. Dude used to steal my clothes. Like, we're friends, you know what I mean? Brothers, even," Mark said.
"So it was really cool to be out here, and it was funny seeing him on the judges table because I haven't been here since he's done that... It was funny!"
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After placing seventh with Sabrina, Mark went on to compete on Dancing with the Stars through Season 6 straight through Season 22. During that time, he finished in first place twice with former figure skater Kristi Yamaguchi on Season 6 and then with Olympian gymnast Shawn Johnson on Season 8.
Mark, who's had many second and third-place finishes over the years, took a break for two seasons in 2016 and 2017, but he returned for Season 25 and competed with violinist Lindsey Stirling. Mark and Lindsey were the runner-up couple that season.
"I have the best partner that I could have asked for, and I'm really proud of what we did today," Charli told reporters in her joint interview with Mark, according to Us.
"And I'm excited for next week, a new style every week. We're starting from scratch again, you know? So it's going to be fun. I'm excited to see what everyone else does."
Mark added, "We go hard in rehearsals. She's really interested in learning the fundamentals of this dance, which is a whole different vocabulary... and I was really proud of her tonight... I saw something that I hadn't seen yet. She was ready tonight!"