Otago, which last won the event at Balmacewen in 1982, has an excellent chance of making the semifinals with good performances against Bay of Plenty and Manawatu-Wanganui today.
Auckland remains on top of the division with three wins, while Otago, Taranaki and Tasman are all half a point back.
Tasman has not won for 15 years, Canterbury for a decade and Taranaki has never had its name etched on the trophy in the event's 60-year history.
But the day was all about the sensational effort by McEwan in scoring a 66, the round of the tournament to date.
McEwan birdied the first hole and then made five birdies in a row, from the ninth to the 13th, on his way to beating the in-form Fox.
The pair fired 11 birdies between them and McEwan's par-busting round led to a narrow result, winning with only one hole to play.
Duncan Croudis, at No 2, continued on his winning way, beating another experienced player, Gary John-Hill, 4 and 3.
Croudis dominated John-Hill from the first hole and made the game look easy for his fourth win from as many outings.
At No 3, Michael Smith led by one after eight holes but lost momentum around the turn, going down to Fraser Wilkin 2 and 1.
Otago's second loss came when Hamish Ireland (No 4) lost to Ben Wallace in 16 holes.
Ireland was in the match for the front nine but Wallace chipped in for a birdie at the 13th hole and Ireland lost the initiative, losing the 14th and 15th.
Simon Hollyer was first out on the course and looked set to post a win at one up playing the final hole.
But Auckland's No 5, Jason Mann, made an impressive birdie 4 on the final hole to snatch the half.
Hawkes Bay leads the other division after the fifth round as it seeks its first title in more than 40 years.
It is among a group of teams showing their teeth with two rounds of section play remaining at Paraparaumu Beach Golf Club ahead of tomorrow's semifinals and final.
With three wins each, Hawkes Bay leads Wellington on a countback of individual games, half a point ahead of Canterbury and North Harbour, with Aorangi and Southland a further half a point back.
Hawkes Bay ran rampant over neighbour Poverty Bay East Coast 4 1/2 to 1/2 yesterday to push to the top of its division while Wellington was forced to work hard to hand North Harbour its first loss, 3-2.
Capital captain Adam Church won the crucial game with a late run.
Canterbury bounced back from a shock loss to Southland on Wednesday to vanquish neighbour Aorangi 5-0 to provide a handy advantage should a countback be required.
It faces a daunting final day with matches against Hawkes Bay and Wellington, while Harbour faces a less hazardous route against winless Poverty Bay and Aorangi.
Taranaki recovered from two losses on Wednesday to grab an excellent 3 to 1 win over in-form Manawatu-Wanganui.
Tasman, beaten 3-1 by Otago in its opening clash on Tuesday, continued the misery for defending champion Bay of Plenty 3-2 to compound the logjam of teams with semifinal aspirations in division one.
