Bruce Ellington's 35-yard catch extended the drive which ended in a 2-yard touchdown run by Lamar Miller.
The Titans made Mariota the second overall pick in the 2015 NFL Draft out of the University of OR, where he claimed the Heisman Trophy.
The Houston Texans rolled over Tennessee 57-14 Sunday afternoon at NRG Stadium thanks to the play of their rookie QB.
Houston's defense forced its first turnover on the Titans opening drive when Hal picked off Marcus Mariota. Watson would end up throwing for 283 yards with a total of five touchdowns on the day.
Mariota went 6-of-10 for 96 yards and two interceptions. Former Bills quarterback Johnny Green also had four passing scores and a rushing touchdown as a rookie in 1960 while the Bills were in the AFL. The Titans trailed 21-7 with 11:44 left in the second quarter. Watson almost led Houston to a shocking win at New England last week by throwing for 301 yards and a pair of touchdowns but he also had two costly picks.
Watson threw two more touchdowns in the second half.
Dylan Cole scored on a 25-yard defensive touchdown after intercepting Cassel to give the Texans a 54-14 lead.
The Titans posted a record of 2-4 against AFC South rivals and they lost twice to the Texans, a big reason why they finished second in the division in 2016. The Texans improve to 2-2, while the Titans fall to 2-2 on the year.