Left-hander Peniston moved to a career-high ranking of 147th in the world after reaching the Queen's quarter-finalsRyan Peniston beat another notable name on British grass by fighting back to overcome French Open quarter-finalist Holger Rune at Eastbourne.
The British men's number six beat world number five Casper Ruud on his way to the Queen's quarter-finals last week.
In the final event before Wimbledon, Peniston, 26, won 4-6 7-6 (7-5) 6-1 against Denmark's eighth seed Rune.
"I'm very happy with that. A tough start but I managed to fight thanks to you guys," he told the home crowd.
"Since Queen's it has been madness. A couple of weeks ago was a lot different and things have changed. But I'm loving it."
Peniston will play a Spanish opponent in the second round, either Alejandro Davidovich Fokina or Pedro Martinez.
Rune, aiming for his first tour-level win on grass to reach the second round, was twice two points away from victory - at 6-5 in the second set and 5-5 in the tie-break.
Four other Britons are playing in the singles later on Tuesday at the Rothesay International, but the headline act is the return of Serena Williams to the court after a year out.
Williams, 40, has not played since she was injured at Wimbledon last year and is competing in the women's doubles alongside Tunisia's Ons Jabeur.
Williams and Jabeur, who is third in the WTA singles rankings, will take on Spain's Sara Sorribes Tormo and Marie Bouzkova of the Czech Republic on Eastbourne's centre court at about 18:30 BST.
That match is preceded by British men's number two Dan Evans' first-round match against France's Adrian Mannarino.
Katie Boulter, the British women's number four, plays against 2021 Wimbledon runner-up Karolina Pliskova in the second round after Peniston's match.
Jodie Burrage meets Spanish top seed Paula Badosa on court one as she looks to eclipse her comeback win over Croatia's world number 80 Petra Martic on Monday - which was the biggest victory of her career by ranking.
Harriet Dart, the second highest-ranked British woman behind the absent Emma Raducanu, takes on Swiss player Jil Teichmann on court two.
