India strengthened their hold on the third and final cricket Test against Sri Lanka, extending their lead to 320 on Day 4 of the match in Colombo today.The visitors were 209 for seven wicket a short while ago.Rohit Sharma who scored 50 off 72 balls, notched up his fourth Test half century as the Men in Blue negotiated the opening session of 37 overs on a wicket which seemed to be easing out.Stuart Binny made 49 runs.India resumed the day at 21 for 3 in their second innings, with a lead of 132 runs.The 3-match series is currently level at 1-all.