At the start of the 1750 season the first 2 races run at Newmarket on 16th and 17th April were a Match race run in Heats and a single race Plate. Dealing with the second of those 2 races first, it was a 50 Guineas Plate for 4-year-olds on the Round Course, each carrying 8st 7lbs.
Tuesday 17th April 1750
1. SNIP, bay colt owned by Mr Martindale and ridden by W Hobrow
2. BLACKLEGS, bay colt by Wilsons Arabian owned by Mr George Prentice
3. UNNAMED chestnut colt owned by Lord Weymouth
4. DRUDGE, bay colt owned by Mr Thomas Panton
Blacklegs had won a 95 Guineas Plate on 6th October 1749 at Newmarket, beating Shakespeare and Pigmy, and was fully expected to follow up in his opening race of the season. Odds of 4/6 and 1/2 were offered on Blacklegs, with between 5/4 and 7/4 offered against the field, and he was entitled to be favourite. Did George Prentice bet against his charge at 7/4? The papers of the day commented, ‘The wise ones were as much mistaken this day as they had been the previous day on Jockey Club Member Lord Gower's horse Little John.’

Turning to the race over heats on the previous day, a 50 Guineas for 6-year-olds and aged horses over 4 miles.
Monday 16th April 1750
1. WHITENOSE, bay horse owned by Lord Portmore 5 1 1
2. SULTAN, bay horse owned by Mr Greville 1 3 4
3. MIXBURY, chestnut horse owned by Mr Curzon 2 4 2
4. LITTLE JOHN, grey horse owned by Lord Gower 4 2 3
5. COLLIER, black horse owned by Duke of Devonshire 3 wdr

FORMLINE
LITTLE JOHN, second in a 50 Guineas race at Newmarket on 27th March 1749, beaten by Mr Thomas Panton’s Bustard.
SULTAN, second in a £50 race at Lambourn on 12th September 1749, beaten in both heats by Babraham. Beaten again by Babraham, when 6th on 19th September 1749 at Burford.
MIXBURY, second in the first heat of a £50 race at Burford on 9th September behind Mr Dutto’s King Pepin, before being withdrawn from subsequent heats, having won a £50 race at Derby 17 days beforehand.
WHITENOSE, formerly Mr Cornwall’s Nonpareil, had shown no previous form.
COLLIER, no previous form of any significance.

Betting on the overall Plate winner
Opening Odds 4/5 Little John, Evens The Field
Had there been bookmakers, in the modern day sense, they would probably have bet:-
4/5 Little John, 4/1 Sultan, 5/1 Mixbury, 100/8 Collier, Whitenose Over round 107%
I wonder if Lord Portmore managed to get a few guineas on Whitenose at big odds?

Betting after Heat 1
After the first heat, in which Sultan defeated Mixbury and Collier, with Little John and Whitenose 4th and 5th but not distanced, the betting would have altered for heat 2.
Betting after Heat 1; 4/6 Sultan, 5/4 The Field
Likely bookmakers odds:- 4/6 Sultan, 4/1 Little John, 7/1 Collier, Mixbury, 100/8 Whitenose (OR 33/1 after 1929 when the Tote was introduced and bookmakers had to be more competitive) Over round 112%
I wonder if Lord Portmore managed to increase his stake on Whitenose at increased odds, or lay the favourite?

An unfortunate setback (These things happen!)
Oh No; Lord Portmore’s friend, and fellow Jockey Club Member, the Duke of Devonshire, withdraws Collier before the heat is run. Without access to his betting book, it is uncertain whether he profited in the betting market from this withdrawal, but surely it is unlikely!!
Betting prior to Heat 2, after the withdrawal of Collier:-
4/7 Sultan, 6/4 The Field
Likely bookmakers odds:- 4/7 Sultan, 7/2 Little John, 6/1 Mixbury, 100/8 Whitenose (over round 107%)
In Heat 2 Whitenose turned the form of the first heat on its head, winning from Little John, Sultan and Mixbury.

Betting before Heat 3
Betting after Heat 2:- 6/4 Sultan, Whitenose 3/1 The Field
Likely bookmakers betting on Heat 3:- 6/4 Sultan, Whitenose, 4/1 Little John, 100/8 Mixbury (Over round 108%)
In the final Heat, with both Sultan and Whitenose requiring one more victory to claim the prize, it was Whitenose who prevailed, beating Mixbury, Little John and Sultan. I guess that is why the newspapers were so astounded by the turnaround in form, and that those in the know would have profited.

Bill O'Gorman comments, ‘Making matches was an art in itself and obviously each party liked to think that they knew something the other did not. There is plenty of intrigue involved. The Old Merlin match saw a pre-run by the trainers with each putting up 7 lbs more than they stated. There are several tales of horses going on tour through the backwoods disguised as wagon horses and stepping into the breach when the racehorse that made the match suddenly went lame. One of the most famous was a match made for Ethan Allen and running mate for a $2000 Purse against Dexter [Dexter is the trotter that is seen as a weathervane] on 21st June 1867. The original running mate went wrong and the match was off but the Ethan Allen team said that they would get another running [galloping] mate and make the match for less money to which the opposition gleefully agreed, as obviously they were sure to win when the pair were not used to going together. By some chance[!] they found a galloper with whom Ethan Allen was perfectly compatible and won a hatful of money from bets in the best of 5 one-mile heats, the first to win 3 heats taking the prize. [This is the origin of the running mate in US elections]’