Raonic won their only FedEx ATP Head2Head meeting in August en route to the Coupe Rogers final in Montreal.
Top seed and 2008 runner-up del Potro knocked out fellow Barclays ATP World Tour Finals contender Nicolas Almagro, the sixth seed, 7-6(7), 7-6(1) in the Tokyo semi-finals. Their first tour-level meeting lasted one hour and 51 minutes.
Del Potro, 25, is through to his 22nd tour-level final after recording his 17th victory in 18 matches at ATP World Tour 500 tournaments.
Del Potro almost took a 3-0 lead against slow-starting Almagro in the first set, before the Spaniard found his footing and fought back under a closed roof at the Ariake Coliseum. In an outstanding opener, which lasted one hour, del Potro saved a set point at 6-7 in the tie-break.
Neither player created a break point opportunity in the second set, which was once again decided by a tie-break. This time, del Potro mixed up his service placement and pinned Almagro deep behind the baseline.
Del Potro dropped six points on serve in the second set and hit 12 aces overall. He goes on to face third seed Milos Raonic.
Almagro, who is in 14th position in the battle for London, dropped to a 35-20 match record on the season.
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