Aaron Willis, Dan Southall and Jake Woodcock scored tries while Brad Darlaston kicked 13 points in a 28-24 victory over the Grantham-based visitors to the Griff & Coton.
Meanwhile the 2nd XV also commenced their new journey in Leicestershire Merit League B with a narrow 21-19 loss at Leicester Vipers II.
Next up for the Manor Park boys on Saturday 14 September:
1st XV (A) versus Mansfield (3pm)
2nd XV (H) v Stoneygate (3pm).