Tries from Hardy (2), Josh Macleod, Ryan Conbeer, Taylor Davies, Jonny McNicholl (2) and Josh Helps, and 14 points from the boot of Dan Jones and Angus O’Brien helped Scarlets to a one-sided 54-10 victory.
Zebre’s points came from a try for hooker Marco Manfredi and five points from the boot of Michelangelo Biondelli.
Scarlets made an excellent start, scoring in 90 seconds when Hardy went over after a break from wing Steff Evans.
And that lead was doubled after eight minutes when a drive from a line-out saw Macleod emerge with the ball for the second try.
Zebre finally got on the scoreboard with a penalty from Biondelli after Scarlets had killed ball in their own 22.
But from the restart, Scarlets grabbed a third try when Conbeer latched on to Steff Hughes’ grubber kick across the line.
It was not all one-way traffic, however, as hooker Monfredi burst over from a line-out to score with Biondelli adding the extra points.
But Scarlets had their try bonus-point in the bag in the 29th minute after Conbeer and Paul Asquith combined to put Hardy over for his second try, despite the hint of a forward pass.
Scarlets started the second half as they had begun the match with an early try as hooker Davies crashed over for a try on his debut. Jones converted as the Scarlets lead was extended to 33-10 in the 43rd minute.
McNicholl picked off Hughes’ little kick ahead to go under the posts for the sixth try after 51 minutes, with O’Brien taking over with the tee.
Scarlets were reduced to 14 players in the 58th minute when Lewis Rawlings was yellow carded as the home penalties mounted, and with the extra man Apisai Tauyavuca thought he had scored a second Zebre try but it was ruled out for obstruction.
Scarlets also had a try ruled out 10 minutes from the end when replacement Dan Davis knocked on in the act of scoring.
But seven minutes from the end, Helps went over by the posts for O’Brien to convert.
And Scarlets had the last say when McNicholl went over for his second, catching O’Brien’s cross-field kick to take the score passed 50.
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