In advising of the split, Tickford has also formally confirmed that it will indeed field three full-time entries in the 2021 Supercars Championship, a reduction of one, and that Jack Le Brocq shifts into the #5 Truck Assist Mustang.
Holdsworth's departure was nevertheless widely expected, with Thomas Randle understood to have been earmarked for promotion to a Championship entry of his own had another Racing Entitlements Contract been obtained.
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The youngster's first stint with Tickford saw him share a Mustang with Holdsworth in the Pirtek Enduro Cup of 2019, the latter's first season at the team.
That pairing produced a podium in the Sandown 500 before Holdsworth picked up another two with Tickford at Sydney Motorsport Park last year.
The now 37-year-old had been renewed on a multi-year contract which took effect in 2020, but the parties have “mutually agreed to part ways” according to this latest announcement.
Tickford CEO/Team Principal Tim Edwards paid tribute to Holdsworth, remarking, “We are very grateful to have worked with Lee the past two seasons, and are equally saddened to confirm we will not be racing together in 2021.
“Along with his ability behind the wheel, Lee's been one of the most well-liked people in our garage and in pit lane.
“Our crew, sponsors, and members have only good things to say about him, and we'll certainly miss having him in the garage and workshop in 2021.
“We wish Lee all the best for the year to come, and look forward to seeing him at the track as a friend in the near future.”
Holdsworth made his Supercars Championship debut in the 2004 enduros with Smiths Trucks Racing and became a full-timer with Garry Rogers Motorsport in 2006.
A first race win came at Oran Park the following year while the second, at Sydney Olympic Park in 2010, capped off a career-best championship result of seventh.
He moved to Stone Brothers Racing in 2012 and entered the history books as the first race winner for Erebus Motorsport, which the outfit had by then morphed into, at Winton in 2014.
A four-year relationship with Team 18 followed, initially in a customer car run by Walkinshaw Racing, and then a mostly frustrating period as a more independent operation.
The Melbourne native subsequently landed at Tickford and, despite initial uneasiness in a Mustang, Holdsworth finished 10th in the championship in 2019 and 11th last year.
He was also on provisional pole ahead of what would be his last start for the squad, at the Bathurst 1000.
Tickford's regular driving line-up going forward is comprised of Le Brocq in the #5 entry which Holdsworth had most recently occupied, last year's Bathurst 1000 pole-sitter Cameron Waters in the #6 Monster Energy car, and James Courtney in the #44 Boost Mobile Mustang.
Courtney moved into the team during the 2020 season suspension after the closure of customer 23Red Racing, which provided its REC for the balance of the campaign.
Said REC is now owned by Brad Jones Racing, which had also been on the hunt for another berth to continue as a four-car concern given Blanchard Racing Team has moved to be independent of the Albury operation.
While there is no room for Randle to get a car of his own just yet, there exists the possibility of wildcard starts this year, and the Super2 Series winner expects to know more about 2022 soon.
Two seats in the Repco Supercars Championship field remain as yet unspoken for, at least publicly, namely one each at Kelly Racing and Team Sydney.