A five-wicket haul from seamer Safyaan Sharif put the hosts under pressure in Colombo and Scotland bowled them out for 107.
Openers Richie Berrington (27) and Calum MacLeod (72 not out) helped put Scotland firmly on course for victory and they wrapped up the win in the 15th over.
The Scots had earlier won and then lost in T20 games against the Sri Lanka Ports Authority over the previous few days.
Scotland coach Pete Steindl said on Monday: "We managed to adapt to the conditions a lot quicker and bowled well. We fielded well today with three sharp run-outs and the guys stepped up to the task.
"Calum and Richie batted well and were aggressive and we managed to rattle off the runs quickly.
"Yesterday was a tough game in very different conditions to the first game. We felt that we could have executed our skills better and got ourselves into a position to pull off a win.
"It was good to get put under that sort of pressure."
- Sports & Recreation
- Richie Berrington
- Sri Lanka Ports Authority
- Safyaan Sharif