The Swans posted a strong total of 273 from 85.5 overs, led by English import Dom Sibley who scored a patient 54 from 151 overs.
Luke Jensen dismissed Alistair Bivens for a golden duck as Gosnells finished 1-3 at stumps after two overs late in the day to cap a fine day for the Swans.
Midland-Guildford focused on working in partnerships, with several stands helping their score.
Sibley was the mainstay, but fellow opener Bevan Bennell (22), skipper Stewart Walters (37) and star player Tim Armstrong (37) helped set the foundation.
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READ NOWThe Swans were 4-151 when all four had departed, but Jackson Wood made a handy 30 before Keaton Critchell capped a dream 24 hours with 36 off 29 balls.
Critchell’s 36 included four sixes and one four in a stunning cameo, which came after running the drinks for Australia in the Second Test against New Zealand at the WACA Ground on Friday.
Play resumes at Sutherlands Park on Saturday at 11.40am.