After a slow start, the 40-year-old Barroso began pressing the action and scored a knockdown in the third round.
However, Romero picked up the action in the fourth round, but then retreated in round five.
In what looked more like a push Romero scored a knockdown in round nine.
After the knockdown, both fighters revved up the action as they traded punches.
However, it came as a surprise when referee Tony Weeks stepped in to stop the fight at 2:41 into the ninth round.
Barroso was ahead on all three judges’ scorecards at the time of the stoppage.
UNDERCARD
Former two-division world champion, 37-year-old Rances Barthelemy 30-2-1;15 won on a majority ten round points decision against Omar “El Relámpago” Juarez 14-2; 5 in a junior welterweight bout.
The scores were 97-93, 98-92 and 95-95.
In a WBA junior welterweight title eliminator, Batyr Akhmedov 9-3; 8 and Kenneth Sims Jr. 20-2-1; 7 went at it in toe-to-toe action through twelve rounds, with Sims winning on a majority decision.
The scores were 114-114, 115-113 and 116-112.
On the same card:
Starling Castillo W10 Esteuri Suero – junior welterweight.
Michael Angeletti W TKO 8 Michell Banquez - bantamweight
Justin Viloria W TKO 4 Pedro Pinillo – junior lightweight.
WBO MIDDLEWEIGHT CHAMPION ALIMKHANULY WINS IN TWO
WBO middleweight champion Janibek “Qazaq Style” Alimkhanuly 14-0; 9 smashed Steven Butler 32-4-1; 26 to defeat in two rounds on Saturday night at Stockton Arena in Stockton, California.
Butler was down three times.
The time was 2:25.
On the same card in a clash for the vacant WBO bantamweight title Jason “Mayhem” Moloney 26-2; 19 won on a 12-round majority decision over Vincent Astrolabio 18-4; 13.
Moloney out boxed Astrolabio in slow motion, which resulted in boos from the crowd.
The scores were 115-113, 116-112 and 114-114.
UNDERCARD
Lightweight Gabriel Flores Jr. 22-2; 8 smashed Derrick Murray 17-9-1; 6 to defeat in 30 seconds of the first round.
Featherweight Ruben Villa IV 20-1; 7 stopped Maickol Villagrana 16-5; 8 in the fifth round. The time was 1:55.
Junior middleweight Amado Fernando Vargas 7-0; 2 beat Bernardo Manzano 2-5; 0 on points over four rounds.
In a middleweight bout Javier Martinez 8-0-1; 2 KOs) and Joeshon James 7-0-1; 4 fought to an eight-round draw.
In a welterweight bout Brian Norman Jr. 24-0; 19 outscored Jesus Perez 24-5; 18 over eight rounds.