Daniel Ricciardo finished fifth, and Nico Hulkenberg was a place below his team-mate in sixth at Monza. The 22 points gathered by Renault has put them right in contention for the "Best of the Rest" spot, currently boasted by McLaren.
Monza saw the latest Spec C engine being used for the first time and if Italy is anything to off, it looks very promising.
"We had a few races where we missed big points, big opportunities," Prost told Autosport.
"There was Monaco, and Spa also, because the pace was good but we lost everything at the start. When you have these kinds of races and problems you get some more pressure.
"Obviously it's not easy, so we had to get some good points, and fourth and fifth is fantastic. We can't do better, anyway.
"It's very good team. There's a lot of work, a lot of pressure, and they deserved this result.
"The pressure is also because we have to be honest, the power was not at the level that we thought we could be this year. We knew that we could not catch the top three anyway.
"You have an objective and if you're not close to the objective, you put on yourself more pressure, which is not very good, because at the end of the day we are still trying to build the team."