Alastair Seeley and Jack Kennedy were involved in a heated exchange after the NI rider piped the Dubliner in the Supersport race at Brands Hatch.
Seeley edged out championship rival Kennedy by 0.026 seconds in an eight-lap restart and out-dragged his rival on the run to the line.
Tempers were high after the chequered flag, with Kennedy kicking out at Seeley on the slow-down lap.
The pair then pushed each but both remained on their bikes.
Seeley’s lead in the championship is now 35 points over Kennedy.
EHA Yamaha rider Seeley, 39, was leading after five laps before the red flag came out when heavy rain started to fall at the Kent circuit.
He held off Kennedy and Brad Jones after the restart, with several riders catching up on the drying track to set up a frantic final few laps.
Kennedy jumped ahead of Seeley on the final lap but the 2011 Supersport champion carried more speed around the final corner to win the drag to the line.
After the line the pair came close to touching and the riders clashed.
“It needs to be sanctioned,” Seeley told Eurosport in relation to the incident, “Lashing out is a bit out of order. There was still room left across the line and I was within the boundaries.
“It felt like someone kicked my bike. For some reason he’s getting frustrated, just like when he got annoyed when I came into the championship last year.
“I do my thing and some people don’t seem to like it. I’m racing for a championship just like I’m employed to do.”
Still frustrated in the post-race interviews, Kennedy called Seeley out for the incident.
“What can I say, the race is dangerous without people doing stupid things,” said the Yamaha rider. “The race finishes after the chequered flag but some people don’t seem to think that.”
Brad Jones completed the podium, with Ben Wilson close to taking his first podium since a crash at the North West 200 in 2015, but had to settle for fifth.
Richard Kerr was the next best of the Northern Irish riders in seventh while Antrim’s Ross Patterson came home in 13th
In British Superbike qualifying Keith Farmer was the top Northern Irish rider in 12th, closely followed by Andrew and Glenn Irwin.
Josh Elliott and David Allingham will line up in 16th and 17th on the grid for race one.