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The second seed overcame Benneteau 7-6 6-3 in 97 minutes to claim his 14th Tour-level tournament.
Del Potro had won 40 successive service games prior to today, but Benneteau broke him twice in the opening set to force a tie-breaker, which the Argentine eventually won 7-2.
The second set was a much more straightforward affair.
Benneteau saved four match points when serving at 2-5, but his efforts were ultimately in vain as Del Potro held to love in the following game to seal victory.