Red flag incidents and worsening weather conditions caused a headache for the organisers, with racing eventually abandoned at approximately 5:25pm with three races still to run.
Only the Supersport race was held over the scheduled six-lap distance on Saturday.
The Superstock race was declared a result after four laps following French rider Fabrice Miguet’s serious crash, while the sole Superbike race was called after two laps in the wake of two stoppages.
Hickman, who won the Superbike and Supersport races, said: “It’s such a shame the rain brought an end to the day but I’m happy for myself and for the team that we got the results we did, whilst it’s also nice to win races at each of the international road races.
“It could have been three wins as I felt really comfortable in the Superstock race and was just biding my time behind Dean before making my move on lap five.
“As soon as I got by, I opened up a lead but with the red flag coming out and the result going back a lap, I had to settle for second.”
After losing out to Harrison in the Superstock race by 0.2 seconds, Lincolnshire rider Hickman took control of the Supersport race on his Trooper Beer/Smiths Triumph, pulling away to win by 7.9 seconds and setting the fastest lap of the race at 128.838mph, which was only two-tenths outside the lap record for the class.
Padgett’s Honda riders Lee Johnston and Conor Cummins horns in a battle for the runner-up spot after pole-sitter Harrison was forced out with a problem.
In a welcome return to form, Fermanagh man Johnston held on in a dash to the finish by a wheel’s breadth, with Adam McLean less than a second behind in fourth on the McAdoo Kawasaki.
Michael Sweeney edged out Paul Jordan for fifth after the pair enjoyed a private battle of their own.
In the Superbike race, the red flags came out when Davey Todd crashed on lap two at the Deer’s Leap on the Burrows Engineering Suzuki.
The 22-year-old fortunately escaped serious injury and was released from the Royal Victoria Hospital on Sunday.
The race was re-started an hour later as the clouds began to thicken and once racing was underway, light rain began to fall on the opening lap.
Hickman took the early lead from Harrison and Cummins, but by the end of the lap, it was Manxman Cummins who led over the line.
Hickman was tucked in close behind with Harrison a close third.
However, Cummins’ race was over on lap two at the hairpin, when he slid off the Padgett’s Honda. Harrison lost a foot peg from his Kawasaki in the incident and was forced into the pits, leaving Hickman clear in the lead from Honda Racing’s Lee Johnston and David Johnson on the Tyco BMW HP4 Race.
On lap three, the race was stopped as the rain increased, with Hickman taking the win by 1.3 seconds from Johnston.
Aussie Johnson completed the podium for the TAS Racing team, with Paul Jordan in fourth on the Dafabet Devitt Kawasaki.