The towering eighth seed said he had been on the verge of pulling out when he injured his already-bandaged left knee after skidding on the fifth point of the match and crashing down in a heap.
But after lengthy treatment and a pain-killing pill the 24-year-old former US Open champion returned to the court to produce one of the best displays of his career.
Using his condor-like wingspan to make up for any lack of movement, Del Potro unfolded his right arm to deliver a barrage of mighty serves and thumping forehands.
His forehand was unplayable at times and it was fitting that he finally broke the dogged resistance of fourth seed Ferrer with his 22nd clean winner from that flank.
"It was the same thing as my third-round match," Del Potro, who injured his knee when falling on Saturday against Grega Zemlja, told the BBC.
"I was very close (to pulling out) because I felt a lot of pain in the beginning of the match, it was exactly the same like I did before. I twisted my knee once again and the doctor gave me some magic pills and I could finish the match."
Del Potro's medical team will work overtime to patch him up for a semi-final against world No.1 Novak Djokovic on Friday.
"I think it's going to be dangerous if I'm not careful in the next few days," he said. "But I played my best tennis in this tournament so far and I'm so happy to be in the semis."
All eyes were on Del Potro's movement in the opening few games and he looked far from mobile as Ferrer tried to stretch him wide, particularly on the backhand side.
Even when fully fit the six foot six inch Del Potro appears to lumber around the court, although his speed is deceptive.
Thunderous Forehands
Forced to take the initiative to avoid getting the runaround by the relentless Ferrer, who will become world No.3 on Monday, Del Potro began unleashing thunderous forehands to leave the Spaniard floundering.
The bandaged Del Potro broke twice to win the first set and clinched the second after Ferrer cracked at 4-4, slicing a weary-looking backhand into the net after another onslaught from the Argentine.
Ferrer seemed to lack the usual spring in his step, possibly because of a toe injury that has been nagging him since reaching the French Open final, but he hung on grimly to force a third set tiebreak.
Del Potro sensed danger when he was 15-30 down on his serve at 4-5 but delivered a towering ace that Ferrer referred to a Hawkeye challenge more out of desperation than genuine hope.
Ferrer fell behind in the tiebreak but again dug deep to put pressure on Del Potro.
There was no escape, however, and after a long baseline rally which had the players scrurrying from side to side, Del Potro launched a forehand missile to clinch victory and this time collapsed to the turf in joy rather than pain.
"I played my best forehand ever in this Wimbledon," Del Potro said. "It was a big performance for me. I am so happy with my level at this moment. I've beaten one of the biggest players of the season."