The 30-year-old O'Connell, a player who gives everything to drag the best out of himself tournament after tournament but is happy out of the limelight, reached his first quarter-final of the season in Bucharest on Thursday with another notable win over the fourth seed, Nicolas Jarry.
The Australian was just two points away from defeat on several occasions in his near-three-hour clay-court slog at the capital's National Tennis Centre, but he held his nerve to prevail 6-2 5-7 7-6 (7-5) after a touch-and-go final-set tiebreaker.
It was the first time world No.87 O'Connell has made the last-eight in any tour-level event since last November's Belgrade Open, but he'll next have to dethrone Hungary's Marton Fucsovics, the title holder, on Friday if he's to make his first semi since another clay-court event in Munich two years ago.
But O'Connell does seem to come alive when the clay-court season dawns, eventually outlasting world No.58 Jarry, who he also beat at last year's US Open when the Chilean was seeded at No.26.
O'Connell will doubtless feel he should have got the job done earlier though as he served at 5-3 in the second set for a straightforward victory, only for Jarry to battle back to drag the match into a decider.
Jarry's firepower may have helped him to crash 35 winners to O'Connell's 18, but the Australian was eventually rewarded for being the more solid of the pair, with the Chilean spraying around 63 unforced errors to his 26.
More concerning perhaps for the Australian was that he needed a medical timeout in the third set for an apparent hip problem as both men began to suffer in the grinding exchanges. Jarry, too, needed treatment to his racquet arm.Â
World No.90 Fucsovics also had to dig deep to keep hold of his title, having to come from a set down to beat Argentina's seventh seed Mariano Navone 4-6 6-4 6-4.
