Ferrer is set to retire after the Madrid Open next month and made a tearful exit on what was his 15th and final appearance at this tournament.
But there was no room for sentiment for Nadal, who won 6-3, 6-3 to take one step closer to a record 12th Barcelona title.
Four of those triumphs came after beating Ferrer in the final and, at the end of this latest victory, Nadal's 37-year-old opponent saluted the crowd before placing his pink headband down on the service line.
"David is not retiring because of his level but it has been a complicated year and a half for him with injuries," Nadal said.
"His level this year has still been very high and for all these years he's been fighting hard and giving us pleasure watching him. We are all grateful to him."
Ferrer reached a career-high ranking of number three in the world in 2013, the same year he went closest to winning a Grand Slam too, undone by Nadal again in the French Open final.
"I gave everything I had," added Ferrer. "I'm very happy, it's a dream come true to play one of my last matches on this court."
Nadal will be gunning for his 12th success at Roland Garros next month and this was more like the sort of form expected of the world number two, who had won 30 consecutive sets in Barcelona before falling one behind to Leonardo Mayer on Wednesday.
"I had to majorly improve," Nadal added. "I need to step up, play with more energy and a different attitude."
Nadal will now face Germany's Jan-Lennard Struff, who knocked out fifth seed Stefanos Tsitsipas, before a potential semi-final meeting with Dominic Thiem, whom he beat in the French Open final last year.
Fourth seed Kei Nishikori is also through after beating Felix Auger-Aliassime in straight sets.
Nadal broke Ferrer for 4-2 in the opening set and was serving for it at 5-3 when rain delayed the match for almost an hour.
But the stoppage could not change the momentum, with Nadal quickly wrapping up the frame upon his return before breaking again early in the second.
Ferrer offered some brief resistance, a backhand winner restoring parity at 2-2 but Nadal raced ahead as a forehand pass and half-volley put him 5-3 in front.
He missed three match points but converted the fourth before finally embracing an emotional Ferrer at the net, around them a standing ovation.