Chasing 250 for victory, the visitors started well but lost nine wickets after the interval for 81 runs as Dawson finished with 5-45 and Felix Organ 3-22 after Mohammad Abbas had taken the crucial wicket of Ben Duckett for 33, writes IAN McCULLOUGH.
After bowling out the hosts for 178 following a delayed start, the visitors were 46-1 at tea only to be bundled out for 127 on a dramatic day on a wicket that Notts skipper Steven Mullaney felt was ‘unacceptable’ for first class action.
The win leaves Hampshire in position to seal a first county title since 1973 – and only their third in 126 years - when they play Lancashire at Liverpool starting next Tuesday.
Hampshire added 45 for their final three wickets to add to their overnight score, after play was delayed until 1pm due to heavy morning rain.
Impressive young all-rounder Liam Patterson-White followed up his first-innings 50 by mopping up the tail to claim his second career five-wicket haul, dismissing Keith Barker (29), Brad Wheal (3) and James Fuller (21) as Hampshire were dismissed for 226.
Openers Haseeb Hameed and Ben Slater got Notts off to a solid start after surviving a testing hour before tea from Barker and Abbas.
The pair survived 40 minutes of the new ball before Abbas got the breakthrough when Organ took a superb diving catch to pouch a bat-pad opportunity off the England opener and send him on his way for eight.
Duckett played the spinners well, sweeping Dawson and Organ with great success, but with tensions beginning to rise in the middle and words being exchanged between the England international and the Pakistan quick, umpire Martin Saggers was forced to step in between the pair.
But Duckett's barbs evidently only seemed to fire-up Abbas, and to his great delight, Saggers' finger went up shortly after his intervention when a ball thumped the left-hander on the pad when it appeared to be drifting down the leg-side.
Dawson, re-introduced into the attack following the dismissal of Duckett, vindicated the faith of skipper James Vince when he had Slater prodding around off-stump and the ball ballooned off his bat and was plucked out of the air by Nick Gubbins at short-leg, reducing Notts to 72-3.
Following Slater's dismissal a procession of batsmen came and went with only teenager Joey Evison reaching double figures as the leaders slumped to a disappointing defeat to drop to third spot on the table with Dawson taking his first five-wicket haul since 2015.
Vince admitted: ‘It's a magnificent win.
‘There were contributions from everyone. I didn't expect it to happen quite as quickly as it did, but we knew that the wicket wasn't as flat as they can be here and was only getting worse.
‘For Daws (Dawson) to get a five-for and Felix (Organ) with his wickets and his runs in the first innings you can pretty much mention everyone, it was a real team effort.
I actually thought 200 was enough, so anything more than that was a bonus
‘I don't know why it was different. With the heavy roller any indentations up the top get taken out, but there seemed to be a few more divots and marks this time. And that time of year the wickets, with the dew, are never quite as flat as you think they are.’
Notts skipper Mullaney added: ‘I don't think we can fault any effort from the lads, I thought at the toss they got it right, but a couple of decisions didn't go our way.
‘If I am honest it wasn't a great pitch; personally I thought it was unacceptable for a first class game.
‘We knew it was going to be a result pitch and Hampshire got it. But we are still in with a chance of winning the County Championship.
‘If we look at it in isolation, we dropped five catches in their first innings and didn't bowl great in the second half of their first innings. But ultimately we weren't good enough and Hampshire deserved the win.’