After agreeing to a reported £60 million transfer for Jacquet in January, the 21-year-old Frenchman's move was confirmed on July 1.
But a niggling knee injury had kept him on the sidelines until the visit of Cesc Fabregas's Como.
The centre-back impressed in the early stages with some well-timed challenges and rounded off a fine first appearance for Liverpool with a tap-in from Cody Gakpo's cross that gave the Merseysiders a 2-0 lead in the 44th minute.
France U21 international Jacquet was replaced by another debutant, Ronald Araujo, at half-time, with Gakpo having given Liverpool the lead in the 23rd minute after good work from Jeremie Frimpong.
"I think Jeremy played really well," Iraola told Liverpool's social media channels.
"Also, Ronald played really well when he came in. When you have two new faces, first game for both, they do so well.
"It was also a very good performance of Jeremie Frimpong, playing 90 minutes as a right-back, helping us offensively but closing very well his side also. So, some good performances at the back."
Ryan Gravenberch came closest to scoring in a lacklustre second half when he clipped the top of the crossbar following fine play by Victor Munoz.
"I think we need a little bit (of) this feeling of finishing with a clean sheet, winning the game," said former Bournemouth boss Iraola, who has succeeded the sacked Arne Slot.
"Still, the first half has been better than the second, but at least we kept our organisation, our composure and we found a way to finish with a clean sheet, 2-0. I think we needed this feeling before we start."
Liverpool begin their Premier League campaign away to Newcastle a week on Sunday.
