Sinner wasn’t at his best again but the world number one did just enough to beat Portugal’s Nuno Borges 7-6 (7/4), 7-6 (7/2), 6-4.
The 24-year-old Italian had narrowly avoided an embarrassing first-round exit when he fought back from two sets to one down to beat Serbian Miomir Kecmanovic on Monday.
The four-time Grand Slam champion ended Carlos Alcaraz’s two-year reign as Wimbledon champion with a brilliant final victory over the Spaniard last year.
He was still some way from those lofty heights against spirited world No. 48 Borges.
Next up for Sinner is a third-round tie against American world No. 81 Jenson Brooksby.
“There’s a couple of things I need to improve. I felt some moments where I still need to get back to this rhythm,” Sinner said.
Andreeva arrived at the All England Club hailed as one of the sport’s rising stars after winning her maiden Grand Slam crown in Paris in June.
But the Russian teenager was unable to maintain the momentum from Roland Garros as Barbora Krejcikova recaptured the magic that inspired her unexpected Wimbledon title triumph two years ago.
The 30-year-old Czech, who also won the French Open in 2021, fought back for a dramatic 4-6, 7-5, 6-4 victory.
“What a match! It’s always been a huge fight against Mirra. I’m extremely proud I managed to win on this beautiful Centre Court, the best court in the world,” Krejcikova said.
World No. 1 Aryna Sabalenka survived a tough second set to dispatch American McCartney Kessler.
The four-time Grand Slam champion won 6-1, 7-6 (11/9), securing a last-32 meeting with former French Open winner Jelena Ostapenko.
“That was a true battle and I’m super happy that I was able to stay in that second set,” Sabalenka said.
Sabalenka has never won Wimbledon, losing in the semi-finals on each of her past three visits.