Carrickfergus rider Alastair Seeley was edged out by Billy McConnell on the last lap of a thrilling Supersport race at Oulton Park on Monday.
The Mar-Train Yamaha rider had crashed out of Sunday's sprint race.
Glenn Irwin was third in Sunday's event and followed that up with a fifth place on Monday to lie second in the series on 63 points, with Seeley third on 61.
Jordanstown man Andy Reid won the National Superstock 600 race and is second in the championship.
Yamaha-mounted Reid, who was 10th in the British Motostar championship last year, is three points behind leader James Lodge.
Reid is hoping to emulate the feats of fellow Northern Irish riders Lee Johnston and Jamie Hamilton, who won the series in 2008 and 2009 respectively, before focusing their attention primarily on road racing.
English rider McConnell completed a weekend double by seeing off the challenge of Seeley and Graeme Gowland in Monday's 16-lapper.
He now enjoys a 13-point advantage over Irwin ahead of the next round at Snetterton in mid June.
"It was a typical Supersport race with no holds barred and we were rubbing fairings and bars," said Seeley afterwards.
"Coming onto that last lap I thought I had it defended well enough. But I started backing in and I didn't want to run in too deep and lose a position that way.
"Billy showed me a wheel and I tried to hold him off and lay on top of him but he pushed me off with his knee."
Meanwhile Fermanagh man Lee Johnston was ninth and Marshall Neill from Portadown 18th in the Superstock 1000cc race.