The tale of two "Harrys'' eclipsed even the return to first-class action of another Aussie, Test allrounder Beau Webster, who also made an encouraging start to his spell with Warwickshire with an unbeaten knock of 32.
Having already been taken into Lancashire fans' hearts as "Harry'', ever-reliable left-hander Harris enjoyed scoring his first century at his new Old Trafford home, finishing the day unbeaten on 165 against Gloucestershire to take his tally to a season-leading 559 runs in just seven knocks.
Across a near four-and-a-half hour, 263-ball chanceless stay, Harris smote 15 fours and two sixes after coming in with Lancashire in a spot of bother at 2-23 in the 11th over.
Adding another ton to the one he scored on his Lancs debut against Middlesex at Lord's, the Aussie's first seven innings for the county have been 138, 52, 43, 50, 77, 34no and 165no.
Harris is the first Lancashire batter to pass fifty on five occasions in his first seven first-class innings for the county.
Lancashire finished the day 5-342, with a double-ton there for the taking for Harris against a Gloucestershire side captained by Cameron Bancroft and featuring Cameron Green.
Meanwhile, the other 32-year-old Australian "Harry'' was working wonders on his Northamptonshire debut as Conway lived up to the extravagant billing his coach, fellow Aussie Darren Lehmann, had given him on the eve of the match, declaring: "Harry is a mad badger, and people are going to love him!"
The Northampton crowd certainly did as they watched the South Australia quick, who has lost his state contract, take 5-68 against Leicestershire.
That included the wicket of in-form visiting skipper Peter Handscomb, trapped lbw for just nine after a 55-minute struggle as his side was bowled out for 304.
Webster became the latest Australian to try to lay down his marker for selection for the World Test Championship final team in June as he made his Warwickshire bow.
The 31-year-old Tasmanian, who made an impressive Test debut against India in Sydney in January, only bowled two overs for 10 runs as Yorkshire were dismissed for just 205 at Headingley.
But with Warwickshire struggling in reply on 5-106, Webster struck five boundaries off 31 balls in his unbeaten counter-attack to help them reach the close on 6-161.
Another Australian debutant for Yorkshire, paceman Jordan Buckingham, proved expensive, going for 51 off eight overs, but he did pick up the wicket of Warwickshire captain and opener Alex Davies.
"I always wanted to come to Headingley as a kid and watch the cricket, so to be out here playing is a dream come true," said the South Australia quick.
Among Yorkshire's England luminaries, Joe Root fell for one, Harry Brook for 33 and captain Jonny Bairstow for 47.
