The hosts’ 231 looked out of reach when Deeping were reduced to 72-4, but some resilient batting from David Sargeant (49), Sam Malton (47) and captain James Hook (45no) saw the visitors home with two overs to spare.
Spalding picked up a second win on the spin by beating the once mighty Bracebridge Heath by five wickets.
Nilantha Atapattu finished with 4-34 as Bracebridge closed on 198-9 before Ethan Lawrence (58no) guided Spalding home.
Bourne are seeking a hat-trick of titles at this level, but back-to-back defeats has given them work to do. Grantham proved 53 runs too good last weekend and Bourne capped a poor weekend by also bowing out of the ECB National Club KO Cup by 107 runs at East Premier League side Sawston & Babraham.
Ufford beat Godmanchester by 98 runs, while Stamford crushed bottom club Waresley by 150 runs.
Tanvir Hussain (57) top scored in Ufford’s 248 all-out. He also took two wickets as Godmanchester were despatched for 147 although Wahed Javed (4-30) did most of the damage.
A ton from opener Alex Birch (109) and 89 from Lewis Spice helped power Stamford up to 302-6 in their 50 overs. The pair put on 184 for the third wicket.
Castor struggled again though. They were shot out for 84 by St Ives & Warboys to complete a 134-run defeat at Port Lane.
Ramsey and March were both beaten in Division One.
Barnack stretched their lead at the top of Rutland Division One to 25 points with a 46-run win over City seconds.
But a couple of the bigger clubs in the area Market Deeping and Wisbech are struggling to raise sides and keep conceding matches. Deeping are currently on -60 points and Wisbech are on -67!
Newborough are top of Division Two after David Cooper’s 105 set up a 157-run win over Whittlesey.
In Division Three Bevan Stokie cracked 110 as Castor beat United Sports by 123 runs. Sam Johnson (35 & 4-15) enjoyed a strong all-round day.