Yorkshire take control
A superb second-morning spell from Ryan Sidebottom and a half-century from Joe Root put Yorkshire firmly in the driving seat against Middlesex.
Root, looking to stake a claim for a place in Peter Moores' new-look England side, hit 63 at Lord's as the Tykes established a commanding 268-run lead.
Earlier in the day, Sidebottom had taken three early wickets and finished with four for 34, prompting another Middlesex batting collapse that saw the hosts bowled out for 123 in reply to Yorkshire's 178.
The visitors then took the game away from their opponents as Root made amends for his first-innings duck and helped his side to 213 for four at the close of play.
Middlesex started the day 64 for three but Yorkshire seized the early initiative when Sidebottom induced an edge from Neil Dexter who departed for a duck in the fifth over.
Joe Denly arrived at the crease and found the boundary with the shot of the morning through the covers but having moved on to seven he was out next ball, caught lbw by Sidebottom.
At 80 for five, the 36-year-old left-armer was in the groove and, ably supported by the excellent Jack Brooks (three for 47), Sidebottom took his third and most important scalp of the morning when he removed Middlesex danger-man Eoin Morgan for 33.
Morgan needlessly played outside his off-stump and Adam Lyth sprang high in the slips to take a brilliant catch and leave the home side struggling even to make three figures.
Yorkshire had their tails up and Liam Plunkett (two for 16) beat the toes of John Simpson (six), clearing out the stumps to make it 95 for seven.
Brooks nearly took the wicket his spell deserved when he drew a nick from Ollie Rayner but the previously agile Lyth put it down.
The right-arm bowler finally got his man though soon after when his full-length delivery sent the bails flying and Rayner walked back to the pavilion on 15 with Yorkshire 107 for eight.
Tim Murtagh (three) came and went after three balls as he was bowled by Plunkett, who then caught Steven Finn (seven) at silly mid-off to wrap up the innings and leave Middlesex trailing by 55.
As the sun emerged from the clouds after lunch, Yorkshire's Lyth and Alex Lees took full advantage as they put on an unbeaten 50 partnership within 13 overs.
Finn (three for 59) and James Harris (nought for 38) did their best to break their opponents' momentum but the opening pair marched on with Lyth particularly prolific, making 33 runs from his first 50 balls.
Right-arm off-breaker Rayner (one for 58) was introduced to contain the visitors' dominance but it was he who found the breakthrough as he clipped the off-stump of Lees who fell for 33.
Lyth secured his third half-century of the season soon after but the in-form left-hander was removed for 54 when he was caught by Rayner off Finn with Yorkshire 96 for two.
The departure of the openers paved the way for Kane Williamson and Root, who nervously scrambled in for a single to get off the mark.
The duo settled quickly though, notching a 50-partnership in 113 balls and 98 overall before Williamson (37) was caught by Sam Robson.
Root seemed to grow in confidence as the afternoon wore on and the 23-year-old was bitterly disappointed when he was eventually caught lbw by Finn for the second day running.
At the close of play, Gary Ballance was unbeaten on 10 while night-watchman Steven Patterson was left on four with Yorkshire firmly in the ascendancy.