Surrey need 249 for victory in their potential title decider against Nottinghamshire after persistent bad light interrupted play on day three at The Oval.
Rory Burns (41 not out) and Dom Sibley (18 unbeaten) took Surrey to 66 without loss at the close after Nottinghamshire, who had resumed on 219-8, extended their second-innings lead to 314 after being bowled out for 256.
Surrey's Matt Fisher followed up his five-wicket haul in the first innings with six for 73 to help leave the top-of-the-table clash hanging in the balance.
Somerset spinner Jack Leach took a season's best seven for 69 to help leave Hampshire bidding to avoid an innings defeat at Taunton.
The home side, who resumed on 381-7, declared on 454-8 - Kasey Aldridge, 149 not out overnight, was run out for 180 - and then sk