Early career

Matsui transitioned to mixed martial arts from pro wrestling and trained at the Takada Dojo for much of his career along with Kazushi Sakuraba. Matsui made himself known for a surprising technical ability and his unorthodox striking, including the use of the shoulder strike from the guard, as well as forward rolls and cartwheel kicks in an attempt to draw his opponents to the ground.^[1] He had his first taste of mixed martial arts when he faced American fighter Wayne Haas in a shoot fight for Kingdom in 1997. Matsui won the fight by decision.

PRIDE

Matsui made his true professional mixed martial arts debut in 1998 at PRIDE 3 against Akira "Mr. Pride" Shoji and the bout ended in a draw. In his next bout at PRIDE 4, he faced future Pancrase Light Heavyweight Champion Sanae Kikuta. This bout also ended in a draw because of the time-limit on bouts in the organization at that time.

At PRIDE 6, Matsui fought against future UFC Welterweight Champion and fan-favorite, Carlos Newton. In an entertaining fight, Matsui fended off increasingly difficult submission attempts from the Brazilian jiu-jitsu specialist and struck when possible, including a notable haymaker exchange at the end of the bout. However, Newton's superior control lost the fight by decision, handing the Japanese fighter his first professional loss via unanimous decision. Matsui fought again at PRIDE 7 against Dutch kickboxer "Dirty" Bob Schrijber, in a fight in which he performed impressively, holding his own against the striker and taking advantage of his superior wrestling skills. Controversy ensued when Matsui was punched in his face while being attended to by the referee because of a problem with his gloves. The two fighters exchanged heated words had to be prevented from brawling before the fight was continued. Matsui continued with renovated aggressivity, performing a takedown attempt which made Schrijber fall through the ropes and brutally land on a table ringside. Well after the bell marking the end of the first round sounded, Schrijber landed a powerful kick to the back of Matsui, who was still down on the ground. The foul immediately resulted in a disqualification win for Matsui, and the first win of his career.

Matsui's next appearance for the organization was at PRIDE 8 where he faced future Pride Middleweight Champion and future PRIDE 2003 Middleweight Grand Prix Tournament Champion, Wanderlei Silva. Outweighed and outmatched from the beginning of the fight, Matsui was rocked with a series of knees from the clinch and punches from Silva, but he demonstrated his heart and continued to battle despite bleeding profusely, even managing to put Silva on his back and land some strikes from the guard, leaving Silva's right eye swollen. He ultimately lost in a unanimous decision, but he passed to history as one of the few opponents Silva wasn't able to finish, including Matsui's own partner Kazushi Sakuraba. However, Matsui then fought against Ukrainian kickboxer Igor Vovchanchyn at PRIDE 9, and he was finished the first time in his career after the referee called a stop to the bout at 5:03 into the first round by an eye cut. Matsui's next bout for the organization was at PRIDE 10 against former UFC 12 Heavyweight Tournament Champion and future UFC Light Heavyweight Champion, Vitor "The Phenom" Belfort. Matsui was handed his third consecutive loss, via unanimous decision.

Matsui returned to PRIDE at PRIDE 14 to fight Brazilian Vale Tudo legend Jose "Pele" Landi-Jons, Matsui being a heavy underdog heading into the fight with a 2-6-2 record. Daijiro started the fight countering a flying knee by catching Pelé mid-air with a front kick, but then he was almost rendered unconscious by another knee strike when he was shooting for a takedown. The Japanese had his back taken with a body triangle, but he recovered from the knee and started countering Pele's submission attempts through sheer heart, driving the Brazilian against the turnbuckle in full runs to fend off rear-naked chokes and dropping him on his head to escape from armbars. Frustrated by his opponent's resistance, Pele landed a series of illegal elbows to the back of Matsui, resulting in a yellow card from the referee which attracted heated words. After the fight was restarted, Matsui took Pelé down and proceeded to attack his guard with ground and pound, throwing shoulder strikes and knees to the tailbone whenever he couldn't throw punches, and also holding Landi-Jons's head and slamming it against the canvas. Through the fight, Matsui's superior wrestling and unorthodox strikes paid off, and he kept control over Pelé while landing consistent punishment from his guard; he also got pops by throwing pro wrestling dropkicks every time the fight went standing. After the match, the judges ruled it a unanimous decision for Matsui, who pulled off one of the biggest upsets in the sport at the time.^[2]

Although Daijiro had challenged Wanderlei Silva to a rematch, his next opponent ended up being Ebenezer Fontes Braga at PRIDE 15 and Matsui lost via unanimous decision. In his next bout at PRIDE 16, Matsui faced the future EliteXC Middleweight Champion, Murilo "Ninja" Rua. Matsui was rocked with many stomps and soccer kicks throughout the bout, and the fight was eventually stopped in the beginning of the third round.

Matsui then fought against future UFC Light Heavyweight Champion Quinton "Rampage" Jackson at Pride 18 and Matsui won via disqualification after he was hit in the groin in the beginning of the fight. Matsui then fought Rodrigo Gracie at PRIDE 19 and lost via guillotine choke submission in the third round. The submission was controversial as Gracie held onto the choke for a significantly long time after Matsui had tapped out. Matsui's next appearance was at PRIDE Shockwave against Dutch kickboxer Jerrel Venetiaan. Matsui lost the bout via split decision after Venetiaan was able to utilize superior striking, especially with powerful kicks. Matsui then fought Rory Singer at Pride The Best Vol. 3|PRIDE The Best Vol. 3 and won via unanimous decision, and then followed this up with another unanimous decision win over Kazuki Okubo at PRIDE 24, which would be Matsui's last appearance for the organization.

In March 2006, Matsui left Takada Dojo along with Kazushi Sakuraba, though Matsui remained in the team as a trainer.

Post-PRIDE

Matsui's next bout was two years later against Ryo Chonan in the DEEP organization and lost in a majority decision before going 0-2-1 in his next three bouts against the likes of Paulo Filho, Brian Foster, and Elvis Sinosic, respectively. In the Pancrase 2005 Neo-Blood Tournament Finals, Matsui picked up his first win in three years with a TKO over Daisuke Watanbe. To date, this is the only TKO/KO win of his career.

Cage Rage

Matsui made his debut for the England-based Cage Rage organization a year later against former Alex Reid and fought to a draw. In his next bout, Matsui faced former UFC veteran Curtis Stout and won via majority decision. Matsui then lost three consecutive bouts before defeating future BAMMA Middleweight Champion and current UFC veteran, Tom "Kong" Watson with an armbar submission, the only submission win of Matsui's career to date. Matsui lost his last fight for the organization against Mark Weir.

Other ventures

Since the demise of the Cage Rage organization, Matsui has exclusively fought in Japan, mostly for the DEEP organization. However, he has struggled, going 3-11-2 in his last 16 fights.