Lancashire top the table after four games after Nottinghamshire lost their 100 per cent record with a draw to Yorkshire, while Worcestershire have lost all of their games so far.
Lancashire, with three wins and one draw, leapfrogged Nottinghamshire after a 147-run victory over Warwickshire.
Batting first, the away side made 227 as Stephen Moore made 67 and Boyd Rankin claimed 5-57.
Warwickshire could only manage 172 in response. Tim Ambrose top-scored with 43, while Ian Bell made 33 and Jonathan Trott 9.
Luke Procter was the pick of the bowlers with 3-33 and James Anderson took 3-57.
Steven Croft's 67 helped Lancashire post 189 second time around, while Chris Woakes took 4-40.
Chasing 245 for victory, the home side were blown away by the spin of Simon Kerrigan (5-7) and Gary Keedy (3-2).
Trott's 39 and Varun Chopra's 29 the only resistance as Mohammed Yousuf made 10 and Bell was out for just 3 runs, giving Lancashire victory by 147 runs.
After beating Yorkshire earlier in the season, Nottinghamshire could only manage a draw this time around, ending their run of three successive county championship wins.
Yorkshire piled on 534-9 declared at Trent Bridge as Jonny Bairstow smashed 205 and Joe Root 95, both career best scores at this level. Paul Franks did his best to restrict the damage with 4-135.
Nottinghamshire were in trouble at 291-8 but recovered to post 428 and avoid the follow-on. Ben Phillips top-scored with 71 not out, Neil Edwards made 64, Alex Hales 59 and Andre Adams 54.
Adil Rashid (3-44), Ajmal Shahzad (3-99) and Rich Pyrah (3-120) each took three wickets.
The game ended in a tame draw, with Yorkshire declaring on 113-2 from 51 overs and setting the home side 220 for victory. Nottinghamshire reached 31-0 from 13 overs before a draw was agreed.
Somerset won their second match on the bounce after two straight defeats as they beat Worcestershire by 91 runs.
Craig Kieswetter's 117 helped Somerset to 309, with Nick Compton (57) and Peter Trego (53 not out) also hitting half-centuries. Gareth Andrew was expensive for his 4-93 from 14.4 overs.
Worcestershire replied with 238, Vikram Solanki top-scored with 69 and Alexei Kervezee made 54. Steve Kirby was the pick of the bowlers with 4-64.
Somerset managed 185 in their second innings as Jos Buttler hit 46 not out and James Hildreth made 44. Damien Wright did the main damage with 6-56.
Chasing 257, Worcestershire lost regular wickets and never threatened the target as they were all out for 165. Solanki made 39 but Gemaal Hussain's 6-33 gave Somerset the win by 91 runs, leaving Worcestershire bottom of the table with four defeats from four games.
Seventh and Eighth place played out a draw as Sussex drew with Hampshire to leave both sides with two draws from four games.
Sussex piled on 438 at the Rose Bowl as opener Ed Joyce hit 103 and Chris Nash 78 in an opening stand of 191. David Griffiths claimed 3-73.
Hampshire responded with 480 thanks to James Vince's 157 and Johann Myburgh's 80. Naved Arif was the pick of the bowlers with 4-70.
Sussex reached 254-6, Luke Wells hitting 100 and Danny Briggs taking 4-99 before a draw was agreed.
Durham face Somerset and Sussex play Nottinghamshire starting on May 10, while Warwickshire host Worcestershire and Yorkshire welcome Hampshire starting on May 11.