Whilst the Millers were losing at Stamford, Boston were looking good for a win having gone 1-0 ahead with 15 minutes remaining.
However Radford levelled and then took the lead in extra time before Boston equalised from the spot to force a penalty shoot-out.
The Lincolnshire side won 4-3 on penalties and will entertain the Millers at the DWB Stadium on Saturday (3pm).
Directions for those going are now on the Away Travel tab.