Tomic, who collected the first ATP title of his career last year in Sydney, saved seven of the eight break points he faced in a 7-6 (7-4), 5-7, 6-3 decision over qualifier Sergiy Stakhovsky in 2 hours, 24 minutes.
Tomic took about two-thirds of the points on serve overall, pushing that percentage to 70 in the final set when he saw only one break point and finished off two of his three break opportunities.
Del Potro, fifth in the world rankings, needed much less time (64 minutes) to get by fourth-seeded Dmitry Tursunov 6-4, 6-2. Del Potro had nine aces and no double faults. He lost only six points in nine games serving.
Del Potro is going against Tomic for a second time in his career, having posted a 6-3, 6-3 win last year in Washington. While Tomic is appearing in his second ATP title match, del Potro is 17-7 with the championship on the line. He was in six finals last year, going 4-2 in those matches.
Saturday will mark the first of two consecutive matches against Top 5 players for Tomic, who learned Friday he opens the Australian Open next week against world No. 1 Rafael Nadal.
The Sydney champion will take home $82,040 while the runner-up earns $43,210. Stakhovsky and Tursunov each won $23,405 as semifinalists.