Sri Lanka captured three wickets, including the prized scalp of Shivnarine Chanderpaul, before lunch to fortify their hold on the opening Test against West Indies on Monday.
At the interval, West Indies, replying to Sri Lanka's first innings total of 476 for eight declared, reached 107 for four with Sarwan unbeaten on 57 and Dwayne Bravo not out on six.
Off-spin legend Muttiah Muralitharan removed Chanderpaul in the last 15 minutes before lunch to deliver a significant blow to the West Indies' batting, after left-arm, fast-medium bowler Thilan Thushara removed Devon Smith and Marlon Samuels in the first hour of the morning.
Thushara has been the most successful Sri Lanka bowler with two wickets for 35 runs from 15 overs.
Thushara struck in the fourth over of the day, after West Indies continued from their bedtime total of 29 for one, and a flat-footed Smith drove lazily at a delivery outside the off-stump and was caught behind for 14.
Sri Lanka tightened their grip, when Samuels ill-advisedly chased a wide delivery from Thushara and was caught behind for five to leave West Indies 58 for three.
But the Sri Lankans were then put on the defensive, when Chanderpaul joined Sarwan and they proceeded to conduct a repair operation.
Sarwan reached his 50, when he turned his 99th ball from Muralitharan between the forward short leg and leg gully fielders to the fine leg region for a deuce.
He and Chanderpaul were progressing steadily to the interval, when Muralitharan struck and remove the latter caught at short mid-off for 23.
Just prior to the interval, Sri Lanka missed a chance to apply further pressure, when Mahela Jayawardene failed to grasp a sharp chance at leg gully from Dwayne Bravo off Muralitharan before the batsman had scored.
Sri Lanka are aiming to win their first Test match in the Caribbean having lost two and drawn two in their previous four. The visitors are also eyeing a Test series victory for the first time in the Caribbean.