|LV= County Championship Division One, Uxbridge|
|Close, day three: Middlesex 338 & 169-2 v Somerset 264-9 dec|
|Middlesex 6pts Somerset 5pts|
Nick Gubbins' unbeaten half century helped Middlesex build a 243-run lead after Somerset declared at Uxbridge.
Nick Compton made an obdurate 94 off 278 balls but then top-edged Steven Finn [3-80] to long leg, and the visitors immediately called a halt on 264-9, still 74 behind.
It looked to have paid off when Alfonso Thomas dismissed Chris Rogers for two.
But Gubbins' career-best 67 and Dawid Malan's 48 boosted Middlesex as they reached the close on 169-2.
Gubbins, covering for England batsman Sam Robson, had already surpassed his previous best in the first innings, when he hit 59.
The 20-year-old's second knock included nine fours and one six and gave his side a good chance of being able to press for a final-day victory.
Earlier, Compton was the glue that held the Somerset first innings together after they resumed on 153-4, although Alex Barrow (36) and Peter Trego (24) made useful contributions.
But the England batsman's long vigil came to a close as when he was caught by Tim Murtagh, denying him a second century of the summer.
Middlesex batsman Nick Gubbins:
"It's gone okay so far, but I've had slight mixed emotions with the previous two fifties because I didn't go on.
"Converting fifties into hundreds is something I'm very keen to learn to do.
"There is a bit of up and down (bounce) with the new ball but it does go soft quite quickly.
"We will have to reassess the situation in the morning and see whether we think spin will play some part."
Somerset batsman James Hildreth on their declaration:
"We wanted to give the indication we are up for a game.
"It's hard to say what sort of target we would chase but wins at this time of the year are crucial."
BBC London 94.9's Kevin Hand:
"The track appears to have reverted to its slower self and forcing a result may be beyond Middlesex, especially after the defiance of Nick Compton.
"Nick Gubbins and Dawid Malan again impressed in the second innings, with both showing fluency on a pitch that has seen most batsman struggle with their timing.
"For Gubbins, it was a third fifty in his first four Championship innings and the 20-year-old is showing a great deal of promise with the maturity of his batting and array of shots.
"Middlesex are unlikely to give the visitors a sniff when they declare and the new ball will hold the key as to whether they can apply pressure throughout the final two sessions of the match."
BBC Radio Bristol's Anthony Gibson:
"This was probably the worst day of Somerset's Championship campaign so far.
"They batted without either judgement or enterprise as they lost five wickets for 106 runs and Nick Compton fell in the 90s yet again after a painstaking effort, occupying 278 deliveries.
"After Marcus Trescothick's surprise declaration, the bowling lacked discipline and consistency as they allowed Nick Gubbins, Dawid Malan and Eoin Morgan to stretch the lead to 243 by the close.
"On a pitch which is lasting well, Somerset will have to bat very badly in their second innings for Middlesex to force the win, but after their first-innings performance, I would not rule that out."