In his last Premier Cricket match before heading back to the UK to take up pre-season training with Somerset, Tom Abell top scored with 16 as the visitors were dismissed for just 98.
Gosnell’s paceman Brett Bayley claimed the wickets of Abell and Jake Carder at the top of the order on his way to 5-33 from 15 overs.
Teammate Matthew Leipold was not far behind finishing with 4-23 from 13 overs.
Jaxom Rose was the only other Gosnells bowler to claim a wicket and it was an important one.
Rose claimed the scalp of Fremantle skipper Ashton Turner who, with Christopher Wood, had steadied the visitors after the early loss of wickets with a 29-run partnership. But when Turner was dismissed with the score on 57 the floodgates opened and Fremantle were soon all-out for 98.
In reply Gosnells were able to recover from its own shaky start to end the day with first innings points in the bag.
After starring with the ball, Leipold top scored with 32 to help the hosts end day one on 6-119, 21 runs ahead with four wickets in hand.
Luke Pomersbach chimed in with 22 runs from 28 deliveries before he was caught off the bowling of Chris Chellew.
Day two will resume this Saturday.