While the international left-hander compiled a superb 125 for Lancashire against Derbyshire at Old Trafford at the start of the second round of championship matches on Friday, other Aussies also hit their stride, headed by Fergus O'Neill's brilliant all-round display for champions Nottinghamshire.
The 33-year-old Harris, who made over 1000 runs for the Red Rose county last summer at an average of more than 60, was soon back in the groove in his first match since the disappointment of losing the Sheffield Shield final with Victoria.
Coming in with the Jimmy Anderson-captained home side struggling at 2-11, Harris batted for nearly four hours and struck 14 fours and two sixes in his 182-ball innings, top-scoring in Lancashire's total of 351.
In reply, Derbyshire lost their prolific Aussie opener Caleb Jewell, bowled for a three-ball duck, as they ended the day on 1-0.
Harris was not the only Victoria player to shine as O'Neill, who made such an early-season impact in Notts' championship charge in 2025, continued where he left off at Trent Bridge against Glamorgan.
The holders were floundering at 6-103 when O'Neill came in at No.8 to launch a counter-attack in a century partnership with Jack Haynes, who went on to make a hundred.
O'Neill cracked 11 boundaries in his crucial 59, as Notts rallied to reach a total of 279.
Glamorgan's new NSW paceman Ryan Hadley, fresh from taking six wickets in his opening match, continued his bright start by taking 4-76, while his Sydney-born Dutch international colleague Timm van der Gugten was equally destructive with his 4-54.
When Glamorgan batted, Test prospect O'Neill then struck twice in his first 14 balls, not giving up a run as he dismissed both their openers, and ended up with impressive figures of 6-4-6-2 as the Welsh county limped to 4-81 at the close.
Test allrounder Beau Webster hit 48 off 70 balls to help dig Warwickshire out of a hole after they'd slumped to 3-22 against Sussex.
With England allrounder Chris Woakes making 64, they managed to reach 267 all out at Hove in the division one clash before the home side replied on 0-17, with Daniel Hughes unbeaten on eight.
Performance of the day came from England prospect Ben McKinney, who gave selectors a nudge by becoming Durham's youngest double-centurion at just 21 with a quickfire unbeaten 214 in their 2-456 against Gloucestershire.
It must have left Gloucester captain Cameron Bancroft rather regretting his decision to invite them to bat.
