Ben Spies took the blame for dropping from fourth to ninth in the early stages of Sunday's Portuguese MotoGP.
The Factory Yamaha star, looking to rebound from eleventh places in the opening races of the year, said that four or five big mistakes caused his decline.
The Texan later regrouped and regained eighth place from Honda's LCR's Stefan Bradl as he took the chequered flag for the first time at Estoril.
“Very mixed emotions today, this is actually the first time in three years that I've finished a race here,” said Spies. “As I told the team, I made four or five big mistakes during the race, they cost me time and places.
“It was a rough race but I'm continuing to build my confidence, I don't enjoy Estoril so I'm happy to have finished.
“ Now we go to Le Mans which is a great event with an amazing crowd, but another track I don't love so much! I'm happy with the bike and its performance so we'll continue to build my confidence and improve the results.”
Team director Massimo Meregalli felt that the first error, which saw Spies run wide, had a knock-on effect.
“Ben had some difficulties during the race, he made a few mistakes, I think the first one put a lot of pressure on him so he was trying to push harder and was unable to,” said Meregalli.
“The most important thing is he got back his feeling and was quite satisfied with the set up which gives us good confidence for the coming races. Tomorrow we will test some new items, let's hope they give us some good results.”
Team-mate Jorge Lorenzo finished second.