Corey Collymore took two wickets as Yorkshire reached 109/3 on day one of Middlesex's final LV= County Championship fixture of the 2013 summer.
Collymore dismissed Adam Lyth and captain Andrew Gale as the former West Indies bowler recorded figures of 2/19 in 14 miserly overs.
Gale was outstanding for Yorkshire - who started the match in second position, one place and 15 points ahead of Middlesex - making 66 after arriving at the crease with his side 1/2 in just the third over of the day.
He was helped by New Zealand batsman Kane Williamson, who made an unbeaten 34 in 124 balls.
Yorkshire's pleasure at having the better of the opening day will have been tempered by the fact that leaders and almost nailed-on champions Durham dominated their full opening day's play against YB40 finalists Nottinghamshire.
Middlesex meanwhile are hoping to earn enough points to secure an impressive second successive third-place finish in only their second season back in county cricket's top flight.