The Centurions saw out day one on 8-330 last Saturday, led by WA rookie Jaron Morgan, who found form at number five with a 107-run innings. Fellow teenager Clint Hinchliffe produced back-to-back half centuries with a knock of 65 adding to his 79 from the last round.
The young pair combined for a 146-run fifth wicket stand to frustrate the hosts, who were on top at 4-101 before Hinchliffe arrived at the crease.
Big Bash hero Craig Simmons, known more for his explosive batting, led bowling figures for the Mariners with 3-87.
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READ NOWRyan Done (2-53) took the important wickets of Morgan and Hinchliffe.
Joondalup will be gunning for its sixth-straight win when play resumes on Saturday.