Marcus Trescothick and James Hildreth each hit centuries before a late collapse meant Somerset were bowled out for 408 on the opening day of the LV= County Championship Division One match against Middlesex at Taunton.
Middlesex captain Adam Voges invited Somerset to bat, but Trescothick, who hit 140, and Hildreth, 187, took Somerset into a good position before the last seven wickets fell for 31 runs.
Trescothick and Hildreth put together a record Somerset partnership for any wicket against Middlesex before Trescothick, having hit 24 fours and a six, was caught at deep midwicket by James Harris off Voges.
Hildreth struck 25 fours and two sixes before Harris had him caught at third man by James Franklin, and the Welshman finished as Middlesex's most successful bowler with a return of 5-83 in 18 overs.
Middlesex reached 10 for no wicket at stumps after Sam Robson and Nick Gubbins safely negotiated four overs.
200 partnership between Trescothick (115*) and Hildreth (98*) from only 225 balls. Somerset 253/2 #SOMvMIDpic.twitter.com/VXbn48FL4K
— Somerset Cricket (@SomersetCCC) April 26, 2015
Voges's decision to field first was possibly influenced by the overcast conditions, but there were few problems against the new ball for Trescothick, acting captain in the absence of Alfonso Thomas, and Tom Abell.
Abell had contributed 16 to an opening stand of 50 with Trescothick when he shouldered arms to a delivery from Tim Murtagh and lost his off stump.
Tom Cooper was lbw for a duck to Harris three balls later, but Middlesex had to wait a further 48 overs for a wicket to celebrate as Trescothick and Hildreth treated the crowd to some superb strokeplay.
Hildreth had a slice of luck on 49 when Gubbins dropped a simple chance at square-leg off Steven Finn, but otherwise played with fluency and style.
WICKET - Somerset 400-7. Hildreth c Franklin (third man) b Harris 187. Five for @James_Harris9#bowledHarry#SOMvMID#TeamMiddlesex
— Middlesex Cricket (@Middlesex_CCC) April 26, 2015
Trescothick survived a sharp chance to Neil Dexter at first slip off Ollie Rayner on 95. That apart, the former England batsman was at his commanding best on the way to his 56th first-class hundred, which arrived with a paddle for two to fine-leg off Rayner.
Hildreth's only century in a disappointing 2014 season for him was the 182 he made against Middlesex at Taunton last August, and he repeated the feat in the 52nd over when he worked Harris away for two runs to deep square-leg.
The breakthrough Middlesex badly needed arrived just before tea when the occasional medium pace of Voges had Trescothick caught in the deep to break a partnership of 261.
Jim Allenby helped Hildreth add 60 for the fourth wicket before his departure, caught behind off Harris for 23, sparked a collapse that saw seven wickets tumble for 31 runs in 11 overs.
482 - James Hildreth has scored 482 runs in his last four @LV_Cricket innings against Middlesex (53, 60, 182 and 187). Thorn. @SomersetCCC
— OptaJim (@OptaJim) April 26, 2015
Harris was the chief destroyer as he had Alex Barrow and Pete Trego caught in the slips, both for ducks, before he ended Hildreth's 212-ball stay in the middle.
Steven Finn accounted for Tim Groenewald, who fenced a delivery to Voges at second slip, and Lewis Gregory was the next to go when taken at mid-off by Finn off Murtagh.
Abdur Rehman, became the fifth Somerset batsman to fall for a duck when Finn wrapped up the innings by having him caught at backward point by Nick Compton.
Trescothick believes his side's batting belied the conditions.
"It was not particularly easy batting out there at times, but we managed to fight through and I was delighted to score a hundred," he said.
"We could have batted a bit longer and taken our innings into tomorrow. But at the same time they showed that if you put the ball in the right places then batting can be quite tricky.
"I think 400 was a pretty good score, but we won't really know how good it is until tomorrow."
Middlesex seamer Harris, who who returned his best figures for the county, said: "I didn't think I was at my best, but I managed to bowl a decent spell towards the end of their innings.
"I've taken a five-for, but I still feel I can bowl better and more consistently.
"We gave them too many balls to hit in the first two sessions, but dragged it back after tea and that was important we didn't let the game get too far away from us.
"Marcus Trescothick and James Hildreth are two very fine players and they played two very fine innings. But we dropped them both and they made us pay."