O'Neill, who's been on duty with Australia A in India, only had a month with the Midlands side back at the start of the championship summer in England in April, but such was his impression in the four matches he played that the paceman proved a key figure in their jet-heeled start to a landmark campaign.
The 24-year-old was only allowed a 28-day stint at the Trent Bridge-based county because of visa limitations imposed by the UK immigration policy for overseas players.
But in that time, O'Neill played a key part in two wins in their unbeaten start to the season -- and it would have been three if rain hadn't ruined his best match of all against Warwickshire at Edgbaston when he took a five-for and scored a half-century.
In all, he took 21 wickets -- the most by any bowler in the country over that period -- at an average of 17.90 and with an economy rate of 2.67. He took two five-fers, and scored 42 against Essex and 50 against Warwickshire.
Nearly five moths later, Nottinghamshire captain Haseeb Hameed was left leading from the front on Thursday as he scored the century against Warwickshire at their Nottingham home that secured the two bonus points they needed to take the title for a seventh time.
Hameed scored 122, setting up Notts to easily pass the 300 they required to get the necessary batting points that put them out of reach of defending champions Surrey, who have relinquished the title after three successful years.
Joe Clarke (52) and Kyle Verreynne maintained the momentum, with the latter bringing up his half-century with a cover drive for four before pulling his next scoring shot for six to get them over the line in style.
Joe Clarke (52), Kyle Verreynne (83) and Liam Patterson-White (70) all chipped in too as Notts posted 374 before reducing their opponents to 3-7 for a lead of 109.
"Anyone who comes ahead of Surrey has played some pretty good cricket because they are really good and it's a great tribute to our players," Mick Newell, Nottinghamshire's director of cricket, said.
Meanwhile, O'Neill, Sheffield Shield player of the season in 2024-25, will be keen to keep making a big impression with the Ashes looming.
Selectors were keen to see him at international level, sending him on the A tour, and he grafted for 1-66 in the first unofficial Test with India A in Lucknow last week on a belting batting strip.
