In a game the home side should have long since decided at Westpac Stadium, Donald's try left Wellington to settle for second in the Championship and lifted Waikato into the Premiership's semifinal spots - for one night, at least.
Waikato will still need Southland to shock Tasman today but, if that result does fall in their favour, they have Damian McKenzie's virtuoso performance to also thank for the mere possibility of a playoff berth.
The first five, released from the All Blacks' camp, looked like the time spent in that elevated environment had enhanced his already abundant skills, creating opportunities with his feet and hands throughout the contest.
McKenzie had a hand in all four of Waikato's tries, sparking his side's attack for their first, laying on the final pass in two more and completing an outstanding tactical kicking game with another late try assist.
That effort, converted by wing Sevu Reece after McKenzie's cross kick with 10 minutes to play, gave Waikato some hope of emerging triumphant from an outing in which they were regularly on the back foot. And, in the frantic final minutes, McKenzie somehow foiled the efforts of three tacklers and found Donald with an offload, allowing the veteran to play match-winner in his first Waikato game of the season.
The visitors, in truth, should have never been in position to stun the Lions. Given the level of dominance Wellington displayed in the first half, the game should have been over by the break.
Such was their control heading into halftime, the home side had enjoyed almost three-quarters of possession while forcing Waikato to make three times as many tackles. Such an arduous outing on defence was always going to take its toll and all three Wellington tries in the half were a result of bruising runs and relentless pick-and-go.
But, instead of sitting pretty at the break, Wellington were in front by only three points. And McKenzie was the unsurprising architect of Waikato's revival, making one big bust up the middle before popping a neat pass over the top of a tackler for Waikato's second try.
The visitors continued their resurgence in the second spell and, suddenly, it was Wellington's defence gasping for breath. They were perhaps fortunate to survive when a debatable forward pass saw Waikato denied after yet another pinpoint kick from McKenzie but, after Asafo Aumua put Wellington back in charge with 20 minutes to play, McKenzie and Waikato weren't to be denied for long.
Wellington 24 (V. Fifita, H. Matenga, R. Goodes, A. Aumua tries; J. Garden-Bachop 2 cons)
Waikato 28 (A. Burn, J. Manihera, S. Reece, S. Donald tries, D. McKenzie 4 cons)
Halftime: 17-14
