The Norwegian seventh seed, who lost last year's showpiece match to Djokovic and the 2022 final to Rafael Nadal, battled past world number 12 Fritz 7-6 (8/6), 3-6, 6-4, 6-2.
The 25-year-old will face Djokovic in the quarter-finals on Wednesday, after the reigning champion's thrilling triumph over Francisco Cerundolo.
"I have nothing to lose (against Djokovic) and I'm going to try and enjoy it," said Ruud. "It's always tough. No matter where you play against him it's one of the toughest matches in our sport.
"I'm going to try and get my revenge but I'm sure he's going to be fit and ready to try and get into the semi-finals."
He trails Djokovic 5-1 in their head-to-head record, but did win their only meeting this year in the Monte Carlo Masters semi-finals.
Ruud has gone on to reach the final each of the three previous times he has made the quarters at a Grand Slam tournament.
He also lost the 2022 US Open final to Carlos Alcaraz.