Moulton Harrox and Bourne 2nd were beaten by the top two in the South Lincolnshire and Border League Premier Division on Saturday.
Grantham and Boston each picked up 20 points, taking the fight for the championship into the final two weeks of the season.
Five points separate these teams with Lindum Ramblers in third.
Grantham secured a seven-wicket win over Moulton Harrox while Boston beat fourth-placed Bourne 2nd by eight wickets after Tom Baxter had taken 5-11 to help bowl Bourne out for 84.
At the bottom of the table, Skegness 2nd lost by five wickets to Long Sutton.
In Division One, just two balls of the match remained when Grantham 2nd claimed a one-wicket victory over Billingborough 2nd to go top of the table.
An unbeaten 33 from number nine Josh Scott pushed Billingborough’s score up to 169-9, Danny Ashley taking four wickets.
Grantham quickly found themselves 15-2 but 46 from Alex Kettle and Ashley’s innings of 35 pushed the score along. However when Ashley became Shane George’s third victim, Grantham were eight down with 26 runs still needed.
Only three runs were added before the ninth wicket fell, leaving final pair Louis Greetham and Rahul Kumar with a tough challenge.
But the bowlers were up to it, chipping away at the total and in a nail-biting finish taking their side to victory.
Grantham 2nd are now 11 points ahead of Spalding 2nd, who were without a game, and 21 ahead of Billingborough - who play Spalding on Saturday.