Half centuries from Nikolai Smith and James Shannon put the Northern Knights in a strong position after a rain-hit first day in the Inter-Pro at Clontarf.
Shannon and Smith shared a second-wicket stand of 132 as the Knights reached 193-2 against Leinster Lightning after 25 overs had been lost.
South African Smith hit a 12-boundary 77 before being caught off Peter Chase.
Shannon was 62 not out from 224 balls with Lee Nelson was unbeaten on 17 at the close.
Lightning perhaps unsurprisingly opted to bowl after winning the toss, but they suffered a major blow as Irish international Max Sorensen was ruled out with illness.
The Knights were without injured regular opener Chris Dougherty, with Muckamore's Jamie Magowan drafted into the side.
With the second new ball due after one over on Wednesday, it promises to be a crucial passage of play in the hunt for bonus points.
Inter-Provincial Championship - Castle Avenue, Clontarf
Northern Knights 193/2 (79 overs) N Smith 77, J Shannon 62 no