Yorkshire lost only Alex Lees during the second morning as they pressed ahead against Lancashire at Emirates Old Trafford, reaching lunch on 141-1 from 50 overs in reply to the hosts' 278.
Lees was trapped lbw by Tom Bailey for 40 to end a 72-run opening stand with Adam Lyth, who went on to record a 121-ball fifty in a second-wicket partnership of 69 unbroken with Kane Williamson.
Williamson was also closing in on a half-century, having reached lunch at 42 not out. Lyth had 54 at this point after passing 6,000 first-class career runs during the morning.
Yorkshire began this afternoon 137 runs in arrears.