Middlesex paceman Tom Helm returned career best figures before skipper Dawid Malan's 23rd first class hundred established a position of strength in the Specsavers County Championship match with Worcestershire at Blackfinch New Road.
Helm finished with five for 36 from 19 overs to earn Middlesex a first innings lead of 65 as Worcestershire were dismissed for 156 in 63.5 overs shortly before tea.
It surpassed the 25-year-old's previous best of five for 59 against Warwickshire at Edgbaston two years ago as he exploited a pitch of uneven bounce and received excellent support from veteran Tim Murtagh (17-9-25-2).
Then skipper Malan and Nick Gubbins cashed in during a marathon final session of 51 overs with an unbroken third wicket partnership of 175.
Malan leg glanced Ed Barnard for four to reach three figures off 121 balls with 14 fours and he accelerated to such an extent that his second 50 came from just 44 deliveries.
He ended the day unbeaten on 107 (138 balls, 14 fours) with Gubbins 72 not out (150 balls, 10 fours) as Middlesex closed on 195 for two, an overall advantage of 260.
Conditions appeared to ease for batting during the second half of the day although Worcestershire, with the exception of skipper Joe Leach, were guilty of some undistinguished bowling.
In a rain shortened morning session Helm followed up his two wickets yesterday with another double breakthrough in the half hour's play possible after Worcestershire had resumed on 64 for three in reply to Middlesex's 221.
Opener Tom Fell had defied the visitors attack for 27 overs on the opening day but added only one to his overnight 18 before he pushed forward to Helm and was bowled.
Helm dismissed nightwatchman Josh Tongue (seven) who fended off a delivery which bounced on him and Nathan Sowter held onto a low chance at second slip.
The players were driven off by a heavy shower and an early lunch was taken at 12.30pm with the total on 85 for five.
When the action resumed, Worcestershire lost two further wickets without any addition to the total.
Riki Wessels (seven) pushed forward to Murtagh and was bowled and then Helm completed his five wicket haul when Ross Whiteley (three) edged to Steve Eskinazi at second slip.
Ben Cox top edged James Harris for six to fine leg and Ed Barnard drove Murtagh for four.
But the veteran Middlesex paceman's next delivery jagged back and accounted for Barnard (six) lbw and Cox (19) was dismissed in the same fashion by Harris.
Resistance came from the last wicket Worcestershire pair of Leach (32 not out) and Charlie Morris (15).
They added 40 in 16 overs before spinner Nathan Sowter trapped Morris lbw.
Leach took the new ball and made two quickfire breakthroughs as Max Holden (two) and Sam Robson (nine) fell lbw in successive overs to leave Middlesex on 20 for two.
But Malan, in his first senior game since recovering from a groin injury suffered on England duty, and Gubbins ensured there were no further alarms for the visitors.
They scored at around four an over and were seldom troubled with Malan first to his half century off 77 balls with six fours.
Gubbins reached his 50 shortly afterwards from 99 deliveries with seven boundaries.
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