The Australia opener was made to work hard for the extra 13 runs he needed at Northampton's Wantage Road ground on Sunday to complete his second successive ton for the Darren Lehmann-coached team.
But a handsome pull off his hips to the boundary off the menacing Naavya Sharma brought him to three figures again off 177 balls.
It just added to his rich vein of form, following the unbeaten hundred he'd made at Canterbury in Northants' previous match and, before that, the half-century he'd compiled as South Australia captain in their Sheffield Shield final win against Victoria in Melbourne last month.
He didn't last too much longer, eventually being dismissed for 107 off 191 balls, having hit 16 boundaries, but his teammate James Sale, with whom he'd shared a 164-run partnership went on to amass a career-best 164 in Northants' total of 409, in reply to Middlesex's 341.
"I was awesome to watch Nathan from the other end, learning from him. He's a class act, isn't he? Back-to-back hundreds, hopefully he can continue that," enthused Sales, whose ninth-wicket partner, Australian paceman Liam Guthrie, also made his first career half-century (51 off 49 balls) in a stand of 74.
When Middlesex batted again, the Sydney-born former England opener Sam Robson was going strong on 49no in their 1-109 as they took a 41-run lead into the final day.
Warwickshire's Tasmanian ace Beau Webster was also in fine nick, falling just nine runs short of his second century for the county as his 91, compiled when his side were ailing at 3-14, bailed out the hosts against Essex at Edgbaston.
The towering allrounder struck 16 boundaries in his classy 123-ball knock, and did most to help ensure Warwickshire could pose Essex a challenging victory target of 206. They were 11-0 at the close.
Another Australian half-centurion during what's turning into an impressive campaign was Jake Lehmann, who made his second 50 of the match for Hampshire against Somerset at Southampton and his fourth half-century in successive knocks for the southern county,
Hampshire had resumed their second innings on 1-146, with left-hander Lehmann, who'd made 76 in his first knock, going on to exactly 50 as he helped the home side compile 336 all out – a lead of 286.
Still, though, Somerset looked in decent shape for a second win of the season in their bid to stay top of division one as they finished the day on 3-139, with James Rew 58no and needing another 148 to win on Monday.
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