"He has got to be the best. He just has so much stamina," May said.
May has driven several champions and he has won the New Zealand Cup with Mainland Banner (2005), Iraklis (1997) and Inky Lord (1989).
He is the most successful driver in the race behind Cecil Devine, who won six times, including three with False Step.
Devine also won with Thunder (1956) and Lord Module (1979).
Monkey King joins 12 other dual winners of the New Zealand Trotting Cup, the previous being Flashing Red in 2006 and 2007.
Two horses have won the race three times - Indianapolis (1934-35-36) and False Step (1958-59-60).
Monkey King will be a 9yr-old next year.
Indianapolis was seven when he won the race for the third time and False Step was an 8yr-old in 1960.
The New Zealand Free-For-All on Friday and the Miracle Mile are upcoming races available for Monkey King.
He won both last year.
A gelding by Sands A Flyin from Tuapeka Vale, trained by Brendon Hill at Kaiapoi, for Auckland owner Robert Famularo, Monkey King has now won 37 races from 76 starts and been minor-placed 20 times.
The $375,000 first prize took his stake earnings to $3,304,999.
Monkey King, who has been slow away in two of his five races this season, began well from the unruly position yesterday.
"He was perfect at the start," May said.
May improved three wide at the 1000m from back in the field to sit outside the pacemaker Smoken Up at the 800m.
Monkey King came ahead in the run home to win by a length and a-half in 4.00.7 compared with his 3.57.3 last year.
Smoken Up held second by a neck from Sleepy Tripp with a length to Power Of Tara, also trained by Hill for Famularo.
The favourite Stunin Cullen broke at the start, went to the lead near the 2300m before fading to seventh.
Franco Ledger was scratched from the Sires' Stakes Final at Addington yesterday after injuring a leg.
"He must have bumped his front leg in the paddock and we will have scanned to assess the damage," Hamish Hunter, his trainer, said.
Mitchell Kerr was fined $400 for careless driving and his drive Toledo relegated from third to 12th in race 12.
Kerr was found to have shifted out on to Hostile Grins on the home turn causing the latter to tangle.
Mark Purdon, the driver of Sleepy Tripp, was fined $400 for pushing out Monkey King at the 1050m in the New Zealand Cup.
Lance Justice was fined $500 for excessive use of the whip on Smoken Up.
Kiwi Ingenuity sustained a severe laceration to her right front fetlock.
She is receiving veterinary attention.
Lord Forbes was treated for a injury to a hind suspensory ligament.
Romulus was a late scratching after being sold.
Jamie Keast was fined $300 for careless driving and his drive Paradise City relegated from third to second last in race 3.
He caused interference to No Courage Russell.
Matt Maguire was disqualified from fourth for breaking for more than 150m in the early stages on race 3.
He has been declared unruly for mobile starts.
Todd Mitchell, the driver of Ima Gold Digger, winner of the New Zealand Trotting Free-For-All, dropped his whip at the 1400m.
