(Reuters) - Carlos Sainz had the thrill of starting his home Spanish Grand Prix on the front row and challenging Max Verstappen for the lead into the first corner but that was as good as it got for the Ferrari driver on Sunday.
While Red Bull's Formula One championship leader romped to his fifth win in seven races, finishing 24 seconds ahead of Mercedes' runner-up Lewis Hamilton, Sainz fell back to fifth place.
At the chequered flag, the Spaniard was 45 seconds adrift of Verstappen.
"I put in even harder work today (than in qualifying) and it doesn't show. Unfortunately this is our situation," he said.
"We know race pace and high speed corners is our main weakness and unfortunately Barcelona has a high degradation Tarmac, a high-degradation configuration and a lot of high speed corners.
"That's why today we were struggling so much out there. I did everything I could, I did the most optimal driving and stints that I could do but unfortunately P5 was the best I could achieve."
Sainz's team mate Charles Leclerc started from the pitlane after qualifying 19th, fighting with the car's handling on Saturday, and finished 11th.
Last year the Monegasque had started on pole position.
Sainz said Ferrari, who brought aerodynamic upgrades to Barcelona, had identified their car's weaknesses and knew exactly what was lacking but it would take time to improve things.
"Mercedes today proved they have done a good step and its a good reference," he said.
"We probably just put the upgrade in the worst possible circuit for us which also doesn't help."
Leclerc said it was clear Ferrari were doing something wrong but he could not understand what.
"I went from a first hard (tyre) to a second hard in the last stint, did exactly the same thing and the car is behaving in a completely different way," he said.
"We have to understand and work. It's been a few races that we are struggling with the conditions or having a very peaky car and today was no better."
(Reporting by Alan Baldwin in London, editing by Pritha Sarkar)