Josh Newton smashed 159 as Spalding secured a second successive win.
They added to Louth’s woes, leaving their opponents 11 points adrift below Boston who were once again involved in the closest game of the day – missing out on victory by just two runs.
Spalding finished on 258-5 and Roy Tilley took 6-42 off 14 overs as Louth were all out for 178 with Matthew Hamilton hitting 81 of these runs.
Market Deeping also picked up their second win of the season at home to Sleaford who were bowled out for 194.
Cephas Zhuwao, newly arrived from Zimbabwe, got 49.
Deeping batted steadily - Josh Smith hitting 75 and putting on 57 for the fourth wicket with Jamie Morgan - then an unbeaten 42 from David Gillett saw the home side to victory.
This moved Deeping up to eighth, on equal points with Alford who slumped badly against fourth-placed Bourne.
Colin Cheer took 7-32 and Jack Berry got 3-33 to bowl Alford out for 65.
Berry finished unbeaten on 48 as Bourne claimed a 10-wicket win.
Grantham moved to the top of the table after a last-over win at home to former leaders Bracebridge Heath.
The visitors were all out for 171 in the 45th over, gifting Grantham five overs, with Matt Lineker hitting 70.
All of the home batsmen got a start but were unable to build sizeable partnerships until at 64-4, Mat Dowman and Dan Webb added 53.
Grantham then fell to 134-7 before Josh Mihill and Sammy Peters got together in a determined stand which took their side to victory in the 55th over with just three balls to spare.
Boston reduced Lindum to 68-6 before the lower order dug in, Tom Lindsay and James Kimber each hitting 32 and number nine Jake Benson finishing unbeaten on 40.
Boston got off to a much better start, reaching 93-2 with Jonny Cheer scoring 69 and at 143-5 they were scenting victory.
But Lindsay joined the attack and his seven overs brought four wickets and, aided by a run-out, Boston were bowled out on the final ball of the match for 174.
Grimsby recovered from last weekend’s heavy defeat to pick up seven points against third-placed Woodhall Spa who made the day’s highest total of 275-8 - Jack Hughes with 55.
But Grimsby put up a determined fight, finishing on 208-9 to hang on to sixth place in the table and leave their opponents one point behind Bracebridge Heath in third.
Meanwhile, the postponed Winkworth Cup T20 final between Bourne and Woodhall Spa will take place at Sleaford on Thursday, June 22, starting at 6.15pm.