The Waratahs scored four first-half tries at HBF Park on Saturday to lead 26-0 inside the first 35 minutes.
The Force outscored the visitors 22-7 in the rest of the game, recording four tries, but never got the deficit below 11.
NSW, who beat Fijian Drua 42-29 last month, will face them again in next Saturday's decider in Ba, Fiji, after the minor premiers beat Queensland 31-5 in Lautoka earlier on Saturday.
Western Force had hooker Hera-Barb Malcolm Heke sin-binned after direct head contact on a Waratahs player in the 19th minute.
The home side had less than 20 per cent of possession and territory after 16 minutes and didn't make their initial thrust into the 'Tahs 22 until the 25th.
Force recently became the first Australian team to beat NSW, but the Tahs bounced back well after back-to-back losses in their last two matches.
NSW made a sizzling start, with Hinds dashing over for a try in the fourth minute following defences-splitting runs from impressive five-eighth Waiaria Ellis and fullback Desiree Miller.
Whitaker got her first five-pointer when she took a cutout pass from Miller after letting the ball bounce into her hands.
On the half hour, Whitaker struck again, taking a ball from Ellis and after crabbing sideways, straightened up and zipped through the defence.
Halfback Hinds ensured the Tahs first half glut of possession was rewarded again, when she sliced through the defence, running over 30 metres for another try.
Heke started the Force rally by muscling over the Tahs line just before half-time.
Trailing 26-7 at the break, the home team came out positively in the second half, with winger Alysha Wigley holding off Miller to score in the corner, though the latter charged down Samantha Wood's conversion attempt.
Influential Miller dashed over for the Tahs fifth try, as they extended their lead to 21.
Force had a rousing final 15 minutes with winger Vani Buleki flying high to catch a high kick from five-eight Grace Freeman to notch the home side's third try and Keira MacAskill adding a fourth in the closing seconds.
