Sussex made steady progress at Hove in their bid to stay in touch with Warwickshire at the top of the County Championship.
In reply to Middlesex's first-innings total of 170 they were bowled out for 287, with Michael Yardy making a patient 89 and then Steve Magoffin and James Anyon adding lusty tail-end runs. Seamer Toby Roland-Jones was the pick of the bowlers, taking 6 for 66.
In reply, Middlesex ticked off most of the deficit in reaching 92 for 2, and with a game in hand they will also hope to stay in touch with the top teams in Division One.
In Division Two, bottom club Leicestershire struggled at Northampton, limping to 187 for 6 in reply to 399. South Africa's two-day match at Derby ended in a draw.