Espargaro and Aprilia have endured a tough year, and after qualifying 13th in Aragon the rider admitted he wanted the season to be over and done with.
But a "super good start" on Sunday lifted Espargaro up to sixth, and he maintained position to post the best result of Aprilia's season, just nine seconds behind race-winner Marc Marquez.
"One of the better days of my career, sincerely," Espargaro said. "It's just sixth place, but I'm struggling a lot this year. It's difficult to maintain the happiness, to stay motivated.
"I was super-focused, riding on the limit, and I didn't make any mistake, even in one single corner, so I'm satisfied with myself."
But Espargaro, who will remain with Aprilia through at least 2020, stressed the result did not mean that the team has turned a corner.
He explained that he and new crew chief Pietro Caprara made significant changes to the bike balance, but that the RS-GP has remained largely "the same".
"The bike, sincerely, is not a revolution because it is what it is but I feel a little bit better, I recover a little bit the aggression," he said.
"I think the people around me, the Aprilia engineers, are clever enough to know which is the level of the RS-GP.
"Many riders rode this bike in the past, and the results are there [for all to see].
"The only one who is able to be competitive [is me], and even like this I'm struggling a lot, so they know that we have to change and improve the '19 bike a lot.
"But I don't care. I go always full [effort], I always give my 100%. I also did a super good race in Misano, and was just 14th place.
"And here I did the same, but in this track I'm stronger and I put sixth place, but still the bike, they [Aprilia] know it's far [from that result]."
Espargaro said that in Aragon he was riding in a way that attempted to compensate for the time the RS-GP was losing on the straights.
"For example, in the last corner after the back straight I braked later than in qualifying, it was every single lap, risking a lot.
"So we need to improve the engine, because I cannot ride like this every weekend, because I will crash 10 [races] of 18."
The Spaniard credited Caprara, who replaced Marcus Eschenbacher as Espargaro's crew chief mid-season, with playing a big part in the Aragon result.
Earlier in the weekend Espargaro had confirmed that Antonio Jimenez - who currently works with Xavi Vierge in Moto2 - was in advanced talks to take over in the role in 2019, but said that he was keen to keep Caprara around in some capacity.