Ireland face a battle to avoid defeat in their first-ever Test against Sri Lanka, who tightened their stranglehold on the second day of the series opener in Galle.Sri Lanka ran up 591 for six declared as Dinesh Chandimal (102 not out) and Sadeera Samarawickrama (104no) followed opening-day centurions Dimuth Karunaratne and Kusal Mendis in going to three figures.Ireland's bowlers lacked a cutting edge and their opponents darted along at four and a half an over before spinner Prabath Jayasuriya took five for 42 as the tourists limped to 117 for seven at the close.Vishwa Fernando did the initial damage with the ball, finding a hint of movement to knock back Murray Commins’ off-stump with his first delivery and the left-arm seamer had two for the over when Ireland captain Andy Balbirnie was snaffled at the second attempt by Nishan Madushka, fielding at short leg.Ireland rebuilt from a humble position of four for two, with James McCollum and Harry Tector putting on 70 but they were left in a heap thereafter, troubled by Jayasuriya’s dip and drift on a turning pitch.Tector and Curtis Campher were undone in the flight and dismissed in the same over and McCollum was bowled by a beauty on 35 which pitched on middle and straightened to brush the top of off-stump.Peter Moor nicked off, with wicketkeeper Samarawickrama completing the catch on a day he registered his maiden Test century, while Jayasuriya had his five-for after pinning George Dockrell plumb in front.Lorcan Tucker, a centurion earlier this month in a losing cause against Bangladesh, resisted and was unbeaten on 21 at stumps but Ireland trail by a mammoth 474 and have it all to do to stay level in the two-match series.