Following the two frustrating weekends in the USA and Mexico, the Spaniard qualified in fourth at Interlagos, one place behind team-mate Lance Stroll.
The team had a frustrating shootout on Saturday, with Alonso tangling with Esteban Ocon and Stroll losing out to the red flag that followed.
However, from 15th and 17th on the sprint grid, they showed good pace as they moved up the field to 11th and 12th in a race that otherwise saw relatively little passing, with Alonso finishing ahead.
"It was hard because the triple race now obviously put a lot of stress on everyone," said Alonso when asked by Motorsport.com about the turnaround.
"It's difficult to analyse data, it's difficult to go back to the factory to reunite everyone. But the team was always working flat out to solve the problems, and to find solutions. And yeah, this performance here in Brazil is going in the right direction."
Expanding on the upturn, he said: "I think especially after this race we have some kind of relief, some weight out of the shoulders from some people, and going into the right direction is a good boost for everyone in the factory.
"And we really needed this type of performance here in Brazil. If we had another weekend struggling maybe that was a little bit worrying, but we always kept pragmatic and doing some tests, some experiments, even if they were painful.
"And hopefully we have a lot of data now to analyse everything."
Alonso said that the sprint pace gave him some encouragement for Sunday's main event.
"Yeah, it was promising," he said. "Definitely we have to execute a good race tomorrow without any mistakes.
"Hopefully a good start with the strategy, and we can go through the first couple of laps without any incident. And yeah, let's see the pace. If it's enough to finish in the top five, top six, whatever, we will take it.
"I think we are more competitive. We are a little bit happier with the car. We seem more competitive as well since FP1, so some extra confidence into the race tomorrow."
