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.
Source: Autosport