Berkshire crashed to a shock 253-run loss at the hands of Cheshire at Nantwich after being shot out for 84 on Tuesday, in only their second Championship defeat since August 2014.
Berkshire had been the favourites to win the Western Division 1 title after they beat defending champions Oxfordshire last month.
They stay second in the table, 21 points behind leaders Oxon, but can overtake them by beating Herefordshire in their final match which starts at the Falkland club in Newbury on Sunday and take at least six bonus points.
Oxon completed their Western Division fixtures with a 254-run win over Dorset at Banbury this week.
There was little hint of the drama that was to unfold at Nantwich when Jonny Connell (31) and Archie Carter (13) launched Berkshire’s second innings with an opening partnership of 30. But they then lost all their wickets for 54 with skipper Dan Lincoln bowled first ball.
Cheshire’s Andy Dufty returned outstanding figures of 11.2-10-2-4 with Andrew Jackson taking three for eight and David Wainwright three for 17.
Former Yorkshire, Derbyshire and Hampshire slow left-armer Wainwright underlined his value to Cheshire by contributing his second unbeaten half-century of the match which meant that Berkshire had to chase 338 in what turned out to be 43 overs.
Imran Malik and Tom Nugent worked hard to stave off defeat, the former scoring just four runs, a boundary, from 40 balls, while Nugent scored a single whilst facing 43 balls before being dismissed.
Berkshire’s defeat wiped some of the gloss off an outstanding performance from slow left-armer Luke Beaven. who took a career-best seven for 87 from 39 overs.
Summary: Cheshire 451-8 and 220 all out beat Berkshire 334-9 and 84 by 253 runs.
By Dave Wright
