Hampshire 539 (Donald 173, Holland 143, Northeast 59, Stone 5-93) and 171 for 8 dec (Donald 52, Hannon-Dalby 3-29) drew with Warwickshire 307 (Hain 129*, Yates 91) and 347 for 8 (Hain 104, Mike 72, Patel 70*, Abbott 5-78)
Hain hadn't scored a Championship hundred for three years coming into the match but after 129 not out in the first innings and 104 in the second appears to have found red-ball form.
He was brilliantly partnered by Leicestershire loanee Mike, who claimed his maiden half-century in any format during a 120-run partnership, as they frustrated Hampshire before skipper Patel led another long partnership with fellow tailender Henry Brookes to complete an incredible rear-guard performance.
The draw means Warwickshire edged further away from the Division One relegation place, as they took nine points from the match, while Hampshire's title hopes took another huge dent despite a 12-point haul.
Hampshire had looked on course for their fourth Championship victory of the season as they needed seven wickets on the final day at the Ageas Bowl. Abbott had taken three wickets in a galvanic evening period on day three, which accounted for both openers, Dom Sibley and Will Rhodes, and nightwatchman Olly Stone.
He almost began the final day in style as Hain edged behind but was spilled by a diving Lewis McManus. Six overs later, Abbott bowled Rob Yates while coming around the wicket to sneak between bat and pad.
In his next over, Adam Hose made the mistake of leaving a straight delivery from Abbott - that left the visitors 52 for 5 and Abbott with figures of 5 for 78, his fourth five-wicket haul of the season.
Hain frustrated Hampshire with a 51-run stand with Tim Ambrose for the sixth wicket. But Keith Barker was rewarded for accurate bowling in both innings against his former county as Ambrose edged to Ajinkya Rahane at second slip.
Hain passed 50 in 77 balls as he teamed up with Mike for the seventh wicket. They provided Hampshire an incredible amount of frustration as they battled through the entire afternoon session, scoring 120 in 40 overs to hand the away side a glimmer of hope.
Hain reached his second hundred of the game, the first Warwickshire player to do so on the road since Ian Bell at Lancashire in 2004, in 188 balls. His previous first-class century came for MCC in last year's Champion County match, while he had not scored one for Warwickshire since the 2016 season - also against Hampshire.
Mike reached his maiden half-century in 89 balls. But the seventh-wicket vigil ended when Ian Holland, with three overs still to bowl until the second new ball, found Mike's outside edge to be caught behind.
Felix Organ then found a ball to turn out the rough and behind Hain's legs to dismiss him for the first time in the match. But the second new ball didn't hand Hampshire the wickets they desired as Patel crunched his first fifty since 2017, in 53 balls.
Patel, with Brookes, held their ground for almost two hours, and 27 overs, to put on 112 for the ninth wicket to secure the draw, with hands shaken with a ball to spare.