“It was an unbelievable tough match, both of us played a lot of sets already so I knew it would be hard. It was a lot of ebbs and flows.
“I thought it was done and he came back from the dead. It was a great battle and two great competitors going at it. That’s what sport is all about.”
Draper, who is the only Briton left in the men’s singles, will look to end 21-year-old Alcaraz’s bid to complete a career Grand Slam on Sunday.
Draper’s childhood rival Jacob Fearnley, who has enjoyed a meteoric rise since turning professional in April, was beaten by German second seed Alexander Zverev earlier on Friday.
Emma Raducanu is the only Briton left in the women’s singles and plays second seed Iga Swiatek on Saturday at 00:30 GMT.
There will be live commentary of that match on BBC Radio 5 Sports Extra.
