It was the first time Houston (3-1) had played without its star defensive end since the 2010 season after Watt , who is out for the season after back surgery, had started 83 straight games since being drafted in 2011.
Fuller also had 81 yards receiving and a touchdown.
The Texans squandered an early 14-point lead and their offense was struggling in the second half when Fuller took the first return of his career for a touchdown to make it 27-20 late in the third quarter.
Fuller, who ran a 4.32 40-yard dash at the combine, took the punt and quickly made a trio of Titans miss before outrunning everyone else down the sideline for the score.
The 21st overall pick in this year's draft was so far ahead of any defenders that he slowed down Usain Bolt-style near the 5-yard line and trotted into the end zone.
It was Houston's first punt return for a touchdown since 2013 and he became the first player in franchise history to have a TD reception and a punt return for a score in the same game. Fuller's 5-yard touchdown reception made it 14-0 in the first.
Clowney, the top overall pick in 2014, sacked Mariota for a 6-yard loss on first down and chased down Delanie Walker after a reception on third down to force a punt.
The Texans raced out to a 14-0 lead after touchdown passes by Osweiler on their first two possessions.
Copyright 2016 by The Associated Press