Reigning champions Comptons failed to pass a target of 109 set by newly promoted South West in the upset of the day in Swindon Evening League Division One.
Pethick, with 29 not out and Grigg, with 21, helped South West to 108-6 and they then bowled out the four-time title winners for 100.
Division One
Match of the week at the County Ground saw Castrol make a creditable score of 167-4 with Addey weighing in with a useful 64.
It was not to be enough, though.
In reply Nalgo reached 168-4, Tamir scoring the season's best so far with 87, supported by Sim with 47.
Nationwide continued their good start and restricted Winterbourne Bassett to 72-8, Thwaites taking 3-15 off his five overs.
Vincent top-scored with 32 and Chattell was unbeaten on 30 as the visitors reached 73 for the loss of only one wicket.
In the other match, Wroughton posted 112-8 and then kept Zurich at bay as they failed by two runs in reaching 110-5.
Division Two
Crosslink continued their fine start with a crushing victory over Wanborough.
Posting 112-6, with Kev Flay contributing 45, they then bowled out the visitors for 28.
Lorne Kitchen helped himself to 81 not out as Talismen reached 147-3 against United Churches.
Churches could only muster 118-4 in reply.
WH Smith must have thought themselves in with a chance when making a more than respectable 133-6 at Nationwide 2nd.
Openers Eddie Roofe and Harris got the home team off to a good start until Harris nicked one behind on 13.
Sherwood (41 not out) then helped Roofe (56 not out) to reach their target of 134-1.
Lydiard Millicent crept to 87-8, but all was not lost and they then held Chameleon to 76-9.
Division Three
Ashbury could not turn their fortunes around and slipped to a second defeat, this time against RPs.
New made 36 as Ashbury only managed 78-7, and in reply the RPs reached 79 for the loss of three wickets.
Mitchell, 59 not out, and Meale, with 50, were the main contributors as Stratton posted 133-2 at Moredon.
Fox & Hounds didn't quite hit the target and ended on 123-4 after a gallant reply.
Division Four
Smith hit 33 not out as Phoenix made 108-6 against Purton, with Norman taking 3-27.
However Purton, back in the league for the first time since 1986, managed to make 109 for the loss of two wickets.
L&K Skips, with Pearson hitting 40 and Dyton 30, made a total of 120-8 against Nine Elms with Harris returning figures of 4-36.
In reply Nine Elms were bowled out for 96.
TOMORROW sees a few mouth-watering encounters in the league.
Comptons entertain Nationwide at the County Ground and high-flying South West have the Nalgo run machine visit them in Division One.
In Division Two, meanwhile, early season favourites Crosslink take on Lydiard Millicent.
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