The 32-year-old champion from Montreal raced on stage to cheers of "GSP, GSP" at the MGM Grand Garden Arena, weighing in at the welterweight championship limit of 170 pounds. He then struck a Usain Bolt-like pose as the crowd cheered.
Hendricks, 30, also weighed in at 170.
Both men smiled as they posed opposite each other, then shook hands and hugged briefly.
"My toughest test ever but don't blink," a smiling St-Pierre said moments later as the crowd roared. "It's going to be a good fight. Tune in (Saturday)."
GSP, of course, makes a cut of each pay-per-view buy as the UFC's biggest draw.
St-Pierre (24-2) has been relaxed all week as he goes after a record 19th UFC win. He has not lost since April 2007 and is riding an 11-fight win streak.
Hendricks (15-1) was just as confident at the weigh-in.
"I'm going to knock him. That all I want to do," Hendricks said to boos. "I want to finish GSP in here. That's my only thing.
"You can boo all you want but you'll be cheering (Saturday).
Fellow Canadian welterweight Rory (Ares) MacDonald, a native of Kelowna, B.C., who trains with GSP in Montreal, was all business as he came onto the stage to weigh in for his fight with veteran (Ruthless) Robbie Lawler.
The two men stared daggers at each other, with Lawler not bothering to put his fists up as they posed. When it ended, Lawler just turned on his heels and left without shaking hands.
MacDonald was 171 pounds, one more than Lawler.
Light-heavyweights Chael Sonnen (206 pounds) and Rashad Evans (205) also did not shake hands even though they are friends and moonlight together as Fox TV analysts. They face off in Saturday's co-main event.
UFC president Dana White had to step in between welterweights Jason (The Kansas City Bandit) High and Anthony (The Recipe) Lapsley when they got too up-close and personal as they squared off.
Bantamweights Erik Perez and Edwin Figueroa arrived with flags — Mexico for Perez, who also wore a wrestling mask, and a combination U.S.-El Salvador one for Figueroa.
All the fighters made weight for the UFC's 20-year anniversary show.