Nick Gubbins celebrated earning his Middlesex county cap by scoring a magnificent century against title rivals Yorkshire.
The opening batsman was dropped on 22 by Azeem Rafiq, one of three catches the visitors spilled, and he made them pay by brining up three figures off 191 balls, reaching the landmark by depositing Ryan Sidebottom into the Grand Stand.
Had it not been for Gubbins' fine knock or Yorkshires slippery hands, Middlesex would have been in deep trouble as the rest of their top six made 57 between them as Jack Brooks took three of the first four wickets to fall.
But the hosts rallied to reach 208/5 before bad light stopped play with 14 overs left in the day.
Middlesex went into the game knowing victory would secure a first title since 1993, while the visitors know that a win may not be enough.
That would be if Somerset won, while obtaining two more bonus points, would send the trophy to Taunton for the first time.
Yorkshire elected to invite Middlesex to bat without the need for a toss and they drew first blood as Sam Robson was trapped in front by Brooks for a duck.
The opening pair of Brooks and Sidebottom were constantly threatening and Nick Compton left alone a ball that was too close to his stumps from the former and was adjudged LBW.
Dawid Malan came in with the intention of playing positively but he chopped on off the bowling of David Willey to depart for 22 and leave the leaders on 57/3.
Stevie Eskinazi steadied the ship as Middlesex went into lunch on 84/3 but he departed a ball after Gubbins reached his half-century.
John Simpson played a watchful innings as he made 15 in a 57-run partnership with Gubbins before he was trapped in front by Tim Bresnan.
Captain James Franklin arrived in the middle and guided the young opener to his century and he reached it with a six off Sidebottom.
The partnership had reached 54 when the umpires brought the players off for bad light two overs after Yorkshire had taken the new ball and the Lord's floodlights weren't allowed to be used.