Dragon Ball is full of memorable battles, with much of the original series revolving around a trilogy of martial arts tournaments between its mightiest warriors. The second World Martial Arts Tournament in the series featured Tien Shinhan as the primary antagonist, with the three-eyed fighter rising through the ranks while representing the Crane School. This put him on a collision course with Master Roshi's Turtle School, including Roshi himself disguised as past champion Jackie Chun. However, Roshi quietly decided to concede during his showdown with Tien, leaving open the question of whether he could've actually beaten Tien if he'd opted to see the fight through.
The entire reason Roshi entered Dragon Ball's first two martial arts tournaments under a disguise and assumed name was to provide his star pupils Goku and Krillin with a stronger opponent to ensure they wouldn't take their training and natural aptitude for martial arts for granted. Roshi barely triumphed over Goku in their first tournament together, with the fighters returning three years later for the next tournament and Roshi's students still none the wiser regarding his true identity. However, joining the tournament this time around was the rival Crane School, headed by Roshi's best friend turned nemesis Master Shen, with Tien as his star pupil and facing Roshi in the tournament's semifinals.
When Roshi and Tien fought against each other, they appeared relatively evenly matched, and Tien eventually realized that Jackie was the disguised Roshi. While Roshi was able to withstand some of Tien's strongest attacks, with Tien resorting to fighting dirty to dish out damage to his opponent, he sensed that Tien represented a new generation of fighters that would provide a better challenge for his students than he could. Advising Tien to reject Master Shen's wicked ways and pursue a nobler path, Roshi quietly jumped out of the ring to forfeit the match, leaving a shaken Tien behind as the victor.
It's never clearly stated in either the manga or anime which of the two fighters is stronger, with Tien claiming to have been holding back his full potential but deducing that Roshi was similarly pulling some of his punches before standing down. The fight in the manga is depicted much closer than it is in the anime, where Roshi is nearly knocked out of the ring in one instance and down for nearly the full ten count in another. In the manga, Roshi regains his bearings after the count reaches five and does not have the same near-ring out as he does in the anime. This implies that the manga Roshi has the fight much more in control than the anime adaptation and could have emerged victorious.
Roshi's entire motivation for entering the World Martial Arts Tournament wasn't to win but simply to test his students on the grandest stage. In a passing comment in the manga, Roshi alludes to the possibility of truly losing to Tien if the fight had progressed as normal but remains as cool and confident as ever at the prospect.
Roshi and Tien have never fought against each other since, instead fighting alongside one another in the climactic Tournament of Power in Dragon Ball Super. This tournament saw Roshi last longer than the younger fighter, with Roshi employing all of his experience and wisdom to stay in the fight longer, and the manga series even demonstrates that Roshi possessed a degree of Ultra Instinct from his commitment to combat. Tien is a mighty warrior, but Roshi's combat-savviness gives him the edge over the physically stronger opponent.
