Cricket is a game of fine margins. If the coin had been angled differently when it hit the Galle International Stadium pitch yesterday, maybe it would have been Bangladesh enjoying a batting-friendly pitch and the Sri Lankans toiling away in the heat.

If Subashis Roy's front foot was a few centimetres behind where it actually landed when he bowled the fourth ball of the first over, Kusal Mendis would have had to go back and Sri Lanka would have been 15 for two.

Instead, at the end of the first day of the first Test, Sri Lanka had established their dominance at 321 for four and Mendis was undefeated on 166 with Niroshan Dickwella looking at ease on 14.

Despite those strokes of misfortune -- self-inflicted and otherwise -- Bangladesh had done well for half the day but having gotten themselves to a position where they were no longer at the mercy of Lady Luck, they let it slip. Unlike in recent matches it was not a spate of dropped catches and missed run-outs that were the agents of Bangladesh's decline, but it was a general dropping of standards in all departments after tea, which Sri Lanka had reached with the score reading 155 for three in 53 overs, hardly a position of dominance.

If catches were not dropped, it was because after tea the bowling was such that the batsmen were always in control. When Taskin Ahmed had Asela Gunaratne bowled off the inside edge by a ball that kept slightly low to end a 196-run fourth-wicket partnership with Mendis, it was very much against the run of play. The Galle heat can be touted as a reason for the Tigers wilting after tea, but inconsistency in standards is not something new to Bangladesh, whatever the climate.

The drop-off from the Tigers was evident as they conceded eight runs from overthrows in the 75th and 77th overs, both bowled by Mehedi, with Asela Gunaratne profiting on both occasions.

Sri Lanka, and in particular Mendis, capitalised handsomely from the steep drop in the Tigers' levels. Mendis hit 18 fours and two sixes in his innings, with the latter two coming near the end of play when he seemed to be scoring runs at will. It took him 100 deliveries to get to 47, but having waited patiently for the bowlers to wilt under the heat, he scored 119 runs off his next 142 balls. Gunaratne was almost as impressive, hitting seven fours in his 135-ball 85.

It was all very different in the morning as the bowlers gave a good account of themselves in the scorching sunshine, extracting two wickets -- those of openers Upul Tharanga and Dimuth Karunaratne -- in the first session. Sri Lanka reached 61 for two in 24 overs, which was one wicket too many after the hosts won an important toss.

Unusually for Bangladesh, not only was the lion's share of bowling done by the seamers, they bowled to a quality that did not make it seem that spinners were needed. Off-spinner Mehedi was brought on with less than half an hour to go for the lunch break.

It was an admirable bowling effort from Mustafizur Rahman, Taskin Ahmed and Subashis. With minimal grass on the wicket, which wore a bleached look under the beating sun, it seemed a wicket to keep the ball full on as some deliveries were taking off at good pace from a good length.

Taskin in particular caused trouble early on, allying his pace with an incisive length, even during a short two-over opening spell. He was replaced by Subashis, and it proved to be an inspired call from Mushfiqur Rahim from his unfamiliar position at mid-off.

Perhaps the only contentious selection in this Test for Bangladesh, Subashis, seemed to be a surprise for Upul Tharanga too. A short ambling run-up does belie the pace he can generate and after a few gentle-paced deliveries, an effort ball skidded off the surface and beat Tharanga's hurried defence and clattered into the top of off and middle to leave Sri Lanka at 15 for one in the fifth over. That was immediately followed by the Mendis let-off, but for a session after that Bangladesh kept the pressure on Sri Lanka.

The second success came less than five minutes before lunch when Karunaratne, after battling for 75 balls for his 30, tried to break the shackles with a cut to a ball outside off stump, but the offering from Mehedi did not spin as much as expected and crashed into the stumps through an inside edge.

Only 29 runs were scored in 15.4 overs after lunch and Mustafizur was operating around the wicket with a slip, a gully, a short cover, a cover and a close mid-off. He was getting just a little shape away from the batsman.

At that point Chandimal, perhaps feeling choked by the field and with only five runs off 53 deliveries, looked for the release valve as a sucker delivery, bowled full and wide, caught the edge of the flashing blade for Mustafizur's good friend Mehedi to take a sharp, leaping overhead catch at gully.

That was when the match turned, and although heat was certainly a factor, it was a continuation of Bangladesh's inability to sustain pressure throughout a whole day unless everything is in their favour that handed Sri Lanka the advantage in the last session.