Karachi, Wednesday: Pakistan thwarted a spirited career-best century by Danushka Gunathilaka to defeat Sri Lanka by five wickets in the third and final one-day international in Karachi on Wednesday, taking the three-match series in the process.Gunathilaka 134-ball 133 lifted Sri Lanka to a challenging 297-9 in their 50 overs but Pakistan chased down the target in 48.2 overs for their first series win in 15 months.