Holbeach United manager Seb Hayes was full of praise for the performance after their first defeat this season.
The Tigers battled for more than an hour with 10 men due to Dan Dougill’s dismissal.
Lewis Leckie levelled from the spot – but Grantham Town won 2-1 with a controversial penalty at the end of the first half.
Hayes said: “We felt that the referee gave everything to them.
“I don’t think Dan deserved a red card for an elbow because he jumped and the other lad went into him.
“After the final whistle, Charley Sanders refused to shake the referee’s hand so he was sent off as well.
“I told the referee at half-time that he was giving them free-kicks and we were getting nothing.
“Our penalty was nailed on and Leckie would have taken two more chances on another day.
“We watched Grantham at Matlock Town on Bank Holiday Monday so we knew what to expect.
“They are two levels above us but we played for 10 men for 60 minutes and still created chances.
If I was at Grantham, I’d feel embarrassed. I thought we stuck to the task and I was so pleased with the commitment, effort and application.Seb Hayes
“If I was at Grantham, I’d feel embarrassed. I thought we stuck to the task and I was so pleased with the commitment, effort and application.
“Our fitness work from pre-season showed and I felt we were better organised.
“Rick Drury made a couple of saves but they were always going to get chances. I thought we nullified their quality.”
The Tigers were also knocked off top spot on Saturday as Leicester Nirvana reclaimed pole position in the ChromaSport & Trophies United Counties League Premier Division.