The day after he cemented his best-ever world ranking at the Geneva Open, the 28-year-old Sydneysider saw a one-set lead disappear against Grigor Dimitrov as he had to give best in a 6-7 (5-7) 7-5 6-4 quarter-final in the Swiss event.
To add further pain after his exit from the warm-up event for the clay-court grand slam, O'Connell was also to learn later that he's landed a dreadful draw at next week's French Open that may well see him have to face the world No.1 Carlos Alcaraz in the second round.
In a gruelling battle that lasted two hours 43 minutes on Thursday, O'Connell eventually got ground down by the Bulgarian star Dimitrov, six years since they last faced each other at the Australian Open.
The victor was to prove the same at Switzerland's oldest tennis club, even though O'Connell had been favourite when he saved three break points in the fourth game and went on to eke out the first set which lasted exactly an hour, edging a tiebreak, before racing into 3-0 and 4-1 leads in the second.
But the world No.33 Dimitrov was up for the battle, recovering the break and earning the key break for 6-5, taking a stranglehold that he was never to release.
The consolation in defeat for O'Connell, even if he didn't manage to make his second clay-court semi-final of the year, was that he'll go into next week's French Open ranked higher than ever before, at No.76.
But how long he'll last at Roland Garros is another matter, after Thursday's draw offered him hope of progress with a first-round clash against Japanese Taro Daniel, the world No.110 before also delivering a second-round sickener.
For the winner will have to face the unenviable prospect of a match with top seed Alcaraz, who also faces a yet-to-be named qualifier in his opener.
The good news is that O'Connell has shown plenty of times already this season that he's willing to go toe-to-toe with the best and never seems overawed.Â
In Munich last month, he beat Olympic champ Alexander Zverev en route to the semi-finals and in the Qatar Open quarter-final in Doha in February gave Daniil Medvedev a real scare in a three-set thiller.
O'Connell and Alcaraz haven't met at tour level before, but when the Australian played the then 16-year-old Spanish phenomenon at a Challenger event in L'Aquila, Italy, three years ago, he was quickly acquainted of the teen's brilliance, losing 6-4 6-2.
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