Santander wound up hitting a double, but Rivero still slammed the door shut with his 20th save of the season to seal the Bucs' fourth straight win.
"The whole day, since the throwing program, I was feeling good," Rivero said, laughing after being informed he came within a hair of touching 103 mph. "I told myself if I got the chance to close it, I'm going to try to push it a little bit.
"I was just throwing everything in there. I was trying to push it a little bit more when it came out. I was good with it."
The fastest pitch of Rivero's season and career had been 102.1 mph, which he hit twice on July 8. The previous high mark in 2017, non-Chapman division, was 102.2 mph, which Red Sox right-hander Joe Kelly hit three times. Chapman has topped 102.6 mph 18 times this season, with a high of 104.2.
Rivero touched 102 mph four times during his 17-pitch outing on Wednesday night, bringing his season total of 102-plus-mph pitches to six, behind only Chapman's 48. Kelly (five times) is the only other pitcher to do it even once.
"Felipe comes in throwing 102. That's impressive," manager Clint Hurdle said. "That's fun to watch."
Entering Wednesday's game, Rivero was tied for third in the Majors with an average four-seam fastball velocity of 98.3 mph, behind only Chapman (100 mph) and Trevor Rosenthal (98.5).
Rivero wasn't the only Pirates reliever to light up the radar gun with a triple-digit fastball, however.
Rookie right-hander Dovydas Neverauskas' first pitch to Seth Smith in the seventh inning was a 100.2-mph fastball, his hardest pitch of the season. Before Wednesday night, the Pirates had two non-Rivero pitches over 100 mph: one by Neverauskas and another by Gerrit Cole.
Neverauskas and Rivero were part of a strong performance by the Pirates' bullpen that could bode well for next season. Jack Leathersich, Edgar Santana, Neverauskas, George Kontos and Rivero recorded the final 12 outs of the game, allowed two hits without a walk and struck out three.
That lowered the bullpen's September ERA to 2.12. While there were a number of factors that led to the Pirates' success in 2013-15, a lock-down 'pen was particularly important to Hurdle.
If the past month is any indication, they could have another strong relief corps taking shape for 2018 -- with the flame-throwing Rivero leading the way.
"It looks like it's heading in a real good direction," Hurdle said.