Worcestershire spinners Moeen Ali and Sachithra picked up a wicket apiece post lunch before Warwickshire's ninth wicket pair of Chris Wright and Boyd Rankin rewrote the record books at Edgbaston.
Moeen struck with the first ball after the resumption when Warwickshire skipper Varun Chopra was adjudged lbw for 107 made off 229 balls with 10 fours.
Senanayake made another breakthrough shortly afterwards when Jeetan Patel was neatly stumped by Ben Cox after making eight with the total 207-8.
But then Wright (61) and Rankin (56) added an unbroken 114 to take the total to 321-8 at tea – the highest partnership for that wcket against Worcestershire by The Bears.
At the start of the day Joe Leach (two) and Charlie Morris (one) collected three wickets for 19 in the space of 32 balls as Warwickshire lost half of their side for 125 and with Sam Hain unable to bat because of a shoulder injury suffered yesterday when fielding.
Leach, fresh from career best first innings figures of 6-73, made the first breakthrough when Laurie Evans (16) drove at the ball and was safely pouched at second slip by Worcestershire skipper Daryl Mitchell.
Tim Ambrose then edged the next delivery just short of Mitchell but the Warwickshire wicket-keeper was soon on his way back to the pavilion.
Leach got the ball to cut back sharply and Ambrose (6) nicked it onto the pad before it ballooned up to Jack Shantry at fourth slip.
In the next over Morris had his reward for a probing spell when he clung onto a caught and bowled chance offered by Rikki Clarke(1).
Keith Barker rode his luck in the early stages against Morris, edging him between second and third slip for two and seeing another false stroke fly away to the third man boundary.
Morris and Leach bowled morning spells of 8-2-26-1 and 9-2-24-2 before being replaced by Moeen Ali and Jack Shantry respectively.
Another change saw Senanayake enter the attack at 183-5 and in his first over a single took Chopra to his century off 212 balls with 10 fours.
Moeen ended a stand of 66 in 20 overs between Chopra and Barker when the latter was trapped lbw for 43.
