The indefatigable O'Connell, one of the busiest Australians on tour in his 10th tournament of the year, earned a handy win in the first round of the ATP 1000 event at the Spanish capital's famous Caja Magica venue on Wednesday, beating Argentinian world No.59 Camilo Ugo Carabelli 6-3 6-4.
The 30-year-old O'Connell, ranked 87, converted all three of the break points he earned and saved seven of the eight he faced to join compatriots Alex de Minaur and Alexei Popyrin, who both had byes, in the second round.
There he'll face US Open and ATP finals runner-up Fritz, the third seed who's competing in his first clay-court tournament of the season after a 2025 campaign dogged by an abdominal injury that's prevented him playing anywhere near his best.
Fritz hammered O'Connell at Wimbledon last year but the 30-year-old Australian will  hope to give the rusty US No.1 more of a run for his money on clay, having already recently reached one quarter-final on the surface in Bucharest.
"It has been really frustrating," Fritz told the ATP before the tournament. "I think this year is the least amount of tennis I have ever played. I haven't been playing in between tournaments because I have been trying to give it time to heal."
Jannik Sinner may still be waiting patiently to return to action amid his doping violation ban but another Italian youngster filled the void on Wednesday when teenager Federico Cina beat Coleman Wong in straight sets.
The 18-year-old Cina, who made his ATP debut with a win over Francisco Comesana in Miami last month, this time won 7-6 (7-5) 6-1 with the help of 19 winners and will next play American Sebastian Korda.
