Lee Johnston claimed his first TT win as Supersport One was stopped after only two laps because of deteriorating weather conditions on Monday evening.
Early leader James Hillier finished second and Peter Hickman third.
Earlier in the day Mansfield brothers Ben and Tom Birchall continued their domination of the TT's sidecar events with a sixth win in a row on Monday afternoon.
A flag-to-flag victory saw the pair win a ninth TT by 48.116 seconds from John Holden and Manx passenger Lee Cain in a new race record.
Alan Founds and Jake Lowther were a further 28.636 seconds down in third, just ahead of Alan's brother Pete and his passenger Jevan Walmsley.
Newcomers Ryan and Callum Crowe came home a remarkable fifth on their competitive debut around the Mountain Course.
The brothers from Jurby threw in a best lap of 113.53, making them the 12th fastest crew in the event's history.
Prior to that the RST Superbike TT was red flagged after an incident at Snugborough at the start of lap three of the four-lap race.
Peter Hickman and Dean Harrison, who had both passed the timing point at Glen Helen, were enjoying a ding-dong battle at the top of the lap charts when the race was stopped.
The race result has since been declared, giving the win to Hickman by 1.7 seconds from Harrison with Conor Cummins in third.
James Hillier, Michael Rutter and Michael Dunlop completed the top six as riders crossed the line at the end of lap two (report in link below).
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9.35am Two-time TT winner and ITV4 presenter Cameron Donald has just posted on Instagram: 'Just been for a lap to assess course conditions. It’s dry roads bright & blustery for this morning's Superbike TT.'
10.40am 10-minute delay because non-race related medical emergency in Ramsey. Superbike race will now start at 10.55am.
10.48am: Further five minute delay - four-lap Superbike race now starts at 11am.
10.55am: Further five minute delay. Start of RST Superbike TT Race now 11.05am.
From the info matrix for riders: 'Conditions good all round the course. Damp patch at Governor's. Wind speeds 25-30mph.'
11.05am: FOUR LAP SUPERBIKE RACE IS UNDER WAY!
- Dean Harrison leads at the first timing point at Glen Helen, 1.150 seconds ahead of rival Peter Hickman. James Hillier is third.
- Harrison holds lead of 1.455 at Ramsey from Hickman. Manxman Conor Cummins up to third.
- Harrison complete opening lap at an average speed of 132.48mph to lead by 1.088 from Hickman. Cummins remains third 4.891 seconds behind Hicky.
- Hillier, Dunlop and Rutter complete top six.
- John McGuinness pulls Norton into pits at end of first lap with oil pressure problem.
- Derek McGee retires at end of opening lap.
- What a second lap! Harrison builds up four-second lead by Ramsey, but Hickman pulls the pin over the Mountain and remarkably leads by 1.7s as they pit at end of lap two.
- Cummins remains third half a minute ahead of Hillier, Rutter and Dunlop.
- Lee Johnston retires at end of lap two.
RED FLAG - INCIDENT AT SNUGBOROUGH
- No restart to be held. Superbike Race result declared at the end of lap two.
- Schedule for rest of the day to be announced.
- Sidecar race to start at 1.30pm.
SIDECAR RACE UNDERWAY
-Tim Reeves/Peter Wilkes and Dave Molyneux/Harry Payne both early retirements.
- Birchalls off to a flyer and lead by 14.904 seconds from John Holden and Lee Cain. Alan Founds/Jake Lowther third.
- Newcomers Ryan and Callum Crowe a remarkable fifth after an astonishing first competitive lap round the Mountain Course of 112.56mph.
- Birchalls stretch lead to 35.559 seconds after a lap of 19 minutes 00.177s, which is just shy of their own lap record. Windy conditions on the Mountain probably denying them a first three-wheel 120mph lap!
- Holden/Cain remain second and A. Found/Lowther third going into final lap.
- Crowes holding firm in fifth.
-BIRCHALLS CLAIM SIXTH SIDECAR TT IN A ROW IN A NEW RACE RECORD!
4.18pm: The roads open car has proceeded from St Ninian's to start opening the roads around the TT course to Lheany Road, Ramsey.
The mountain section of the TT course will not be opening between 5pm to 6pm.
Roads will be closing again at 6pm.
6.30pm SUPERSPORT RACE ONE UNDER WAY.
- Lee Johnston claims his first #IoMTT win, as Supersport One is stopped after only two laps because of deteriorating weather conditions.
Early leader James Hillier finished second and Peter Hickman third.
- Dean Harrison fourth, Michael Dunlop fifth and Conor Cummins sixth.
- Rest of the evening's planned qualifying scheduled cancelled because of the weather.
- Roads to open soon.
7.29pm The roads open car has left St Ninian's to proceed opening roads on the TT course through to Lheaney Road, Ramsey.