Honda F1 managing director Masashi Yamamoto has paid credit to Max Verstappen's role in aiding the manufacturer's development through the 2019 season.
Red Bull took the plunge with Honda for the 2019 season, ending a 12-year relationship with Renault in the process.
It paid off to the tune of three race wins for Verstappen in Austria, Germany and Brazil, as well as the first two pole positions of the Dutchman's career.
The results came as a sharp contrast to Honda's miserable spell as partners with McLaren, and the Japanese manufacturer said Verstappen's role in the success could not be underestimated.
Yamamoto told Motorsport.com: "From Spec 1 to Spec 4, everything went smoothly on schedule, as planned.
"We can say that with Red Bull, a good team, and Max Verstappen, a very good driver who gives us very good feedback, they have powered our development and made it smoother to proceed."
Honda introduced three upgrades across the 2019 season, with the biggest step-up saved for the final update of the season, boding well for a 2020 season in which Verstappen has targeted a title tilt.
"During this season we started with the Spec 1, and the step to Spec 2 is minor," F1 technical director Toyoharu Tanabe told Motorsport. "Then we stepped up to Spec 3, a bigger step than Spec 1 to Spec 2. And then Spec 4 was bigger than Spec 2 to Spec 3.
"We are happy to introduce our PU as we promised with the team and drivers, it was almost the same step we could make during the season that we told the team.
"From the trackside point of view, as a technical director at the trackside, I'm so happy with that power unit progress."