Gautam Gambhir notched up his seventh century while Virat Kohli struck his maiden to script India's series-clinching seven-wicket win over Sri Lanka in the fourth cricket ODI in Kolkata on Thursday.Chasing 316 to win the tie and seal the series with one match to go, India found themselves in the morass at 23 for two before Gambhir (150 not out) starred in an 224-run stand with Virat Kohli (107) to inject fresh life into the chase and then completed the formality in Dinesh Karthik's (19 not out) company.Gambhir, who became the newest member of the 3000-run club, faced 137 balls in his controlled innings, hitting 14 fours in the process. Kohli's mature 114-ball knock was studded with 11 fours and a six.Earlier, Upul Tharanga (118) hit his seventh ODI century and starred in a 126-run partnership with captain Kumar Sangakkara (60) as Sri Lanka posted 315 for six, the highest score at the venue till India overwhelmed it.