Durham duo Mark Stoneman and Scott Borthwick made Middlesex suffer as there were runs aplenty in the top tier of the LV= County Championship.
Division One leaders Middlesex may now be regretting their decision to bowl first after winning the toss, as they saw the reigning champions reach 411-4 by the close of play at Durham Emirates ICG.
Stoneman (187) and Borthwick - who was unbeaten on 164 at stumps - put on 274, the highest second-wicket stand for Durham against any opposition in first-class cricket.
Their alliance was eventually ended when Paul Stirling's off-spin accounted for Stoneman, the opener having hit 26 fours to post the highest score of his career. He had already dominated an opening partnership of 82 with Keaton Jennings.
Ben Stokes contributed 23 before being bowled by fellow Ashes tourist Steve Finn but none of the Middlesex bowlers could find a way to shift Borthwick, the left-hander hitting a six and 21 fours.
There were centuries for two Yorkshiremen at Wantage Road, Adam Lyth and Alex Lees sharing in an unbroken alliance of 237 to put their team on the front foot against Northamptonshire.
Having started their second innings trailing by 115 runs, Yorkshire's opening duo not only wiped out the deficit but put their team into a lead of 122 by the halfway stage of the contest.
Lyth made 116 not out from 222 deliveries while Lees, who was dropped on 78, was unbeaten on 105 having faced 242 balls. The White Rose county had managed just 136 as a team in a first innings that lasted just 40.3 overs.
Northamptonshire had resumed on the second morning on 191-7 and were able to extend their advantage into three figures thanks to a half-century from Ben Duckett (51) before Adil Rashid wrapped things up, claiming the last two wickets to fall.
Somerset were another side in Division One to pile on the runs, ending the opening day of their clash with Lancashire at Old Trafford on 312-3.
Johann Myburgh (35) and Marcus Trescothick (55) gave the visiting county a solid start, but it was Nick Compton and Alviro Peterson who punished the home attack with a superb third-wicket partnership worth 195.
Compton fell in the 90s for the second successive Championship match, departing nine runs short of three figures when he was bowled by Kabir Ali. Peterson, however, reached the close on 109 not out.
Samit Patel was a centurion himself in Sunday's action as bat dominated ball, the all-rounder furthering his claims for a place in England's Test squad for the upcoming series against Sri Lanka with 142 not out for Nottinghamshire.
Phil Jacques weighed in with 67 and Chris Read made 62 not out as Notts compiled 408-5 against a Sussex bowling line-up that saw debutant Matthew Hobden claim two wickets.
There was also a pair of scalps for all-rounder Luke Wright, but it was an otherwise difficult day for the home team at Hove after they had decided to put the visitors into bat.
Patel - who played the last of his five Tests against India back in the winter of 2012 - found the boundary 23 times as he recorded his second first-class century of the summer, moving him past 600 runs already for the season.