Sinner’s most recent five-setter came at Roland Garros, where as the red-hot title favourite he led Juan Manuel Cerundolo 6-3 6-2 5-1 before fading to a shock defeat.
In his first official match since that unexpected result, Sinner showed some understandable signs of nerves and rust as he played Wimbledon for the first time without a grasscourt tune-up event under his belt.
Leading 40-0 at 4-4 in the first set, the top seed suddenly lost nine points in a row to drop the opener.
Having survived a nasty-looking slip in the third set, he held a set point in the subsequent tiebreak before Kecmanovic snatched three points in a row to move to within a set of victory.
It was also during the third set when patches of Sinner’s white shoe began turning red with blood, which he confirmed was caused by his nail.
“One fall is a tough one because you can get injured,” Sinner said. “I got lucky there because things can go wrong very, very quickly. I try to still trust in my movement. Also third, fourth and fifth set was very important to keep moving in a very natural way, which I did.
“I’m very glad nothing happened.”
The defending champion steadied, breaking in the sixth game of the fourth and fifth sets to progress.
It marked the first time Sinner had been stretched to five sets in the opening round at a Grand Slam tournament since the 2022 US Open.
“The plus-one shot of him today was very, very strong. Even though sometimes I returned very well, he was always playing the first ball very well, and I struggled a bit. So that’s something where we need to improve,” said Sinner, who avoided becoming the first defending Wimbledon men’s champion to lose in the opening round in 23 years.