Alonso finished the Spa race in fifth place, beating the Mercedes of George Russell and the surviving McLaren of Lando Norris.
The solid result followed huge frustration on Saturday, when the Spaniard qualified only 15th in the shootout after team-mate Lance Stroll brought out a red flag, and then spun off early in the sprint.
In the main event he jumped up from ninth to sixth on the first lap, gaining another spot when countryman Carlos Sainz fell back due to accident damage.
“I think the car felt fast today,” said Alonso when asked by Autosport about his strong form on Sunday.
“The guys did an incredible job again on the strategy, also on the pitstops. We made a few places also yesterday, even if we didn't finish the race. And yeah, I think today the car felt more normal.
“So we had a few thoughts after Hungary, after Silverstone. So the team was making a few set-up changes also to the car. And I think it paid off today. The car felt more normal, more competitive. So yeah happy, and a good boost for summer.”
Alonso admitted that it hadn’t been easy to get everything right on a tricky rain-hit sprint weekend.
“I felt definitely more competitive than the last few events,” he said. “It was not an easy weekend to go into the rhythm, and the wet qualifying and track changing all the time. So not much experience on dry.
“I think, apart from McLaren, we were all on the dry set-up, or dryish. We never did two laps with the same conditions all through the weekend. It was just getting drier and drier, and eventually into the slicks. And that was all about qualifying, the sprint format is always like that.
“And yeah, I was lucky at the start. Before Eau Rouge I made a few places there, and I was a little bit worried if we will fall back, and the pace will not be good enough to keep that position.
“But it was good, today the car felt fast. We kept one Mercedes behind, one McLaren behind. So we were in the mix. And that's good news before the summer break.”
Alonso, who turned 42 on Saturday, conceded that experience is invaluable in circumstances such as sprint weekends.
“I’m nearly 43 you can say now!," he joked. “I think people already saw that it's not a big change when you're 41 or when you're 25. It's more in your head, in the motivation, how you approach the weekend.
“And yeah, races like today or the starts of today, or even a few examples in other teams, they bet more on experience, like Daniel [Ricciardo] now in AlphaTauri, and things like that. So it's not about youth, it's just about going fast.”
Reflecting on the first half of the 2023 season he said: “Incredible. A dream first half of the season, we are P3 in the constructors’ championship in front of Ferrari, we are P3 in the drivers’ championship together with Lewis. It was impossible to think this way in Bahrain.”
