Rockingham-Mandurah are sitting in a good position for day two of their clash with Perth.
Perth won the toss and sent the Mariners to bowl on day one, getting all out for 292.
The pick of the bowlers was Adam France with 4-76 off 17 overs.
"We got off to a good start... we managed to get a few breakthroughs and had them at 5 for 110," coach Kris Kennedy said.
"[Perth's] middle order really dug in for them... this drove them to a pretty competitive total.
"The boys are looking to finish the season strong, so I'm looking forward to a big effort this weekend."
The Mariners go in to day two at 1/35, which gets underway at Lark Hill Sporting Complex on Saturday.