Farnham have played far better this season, but, in the words of head coach Norman Gray: "We did just enough to win.
"It was the forwards who got us through," he added. "All four tries came from line-outs and rolling mauls. After going 15 points up, we took the foot off the accelerator and didn't knuckle down.
"But we won – two years ago we would have lost. That's how far we have come."
The previous week, Farnham had recorded a superb league win at Purley, despite being decimated by Max Falkiner's wedding. The key players were all back this week, except for pack leader Falkiner, yet Farnham struggled to subdue Middlesex 1 side Feltham.
Three pushover tries gave Farnham a comfortable cushion: a line-out, a catch from Farnham's throw, the trundle to the line, and a hand to the ball. Farnham worked this routine to perfection.
But as the home side eased up, Feltham fought back to 10-15 and Farnham were relieved to get the fourth forwards' try in the last 10 minutes.
In an erratic Farnham display, four players stood head and shoulders above the rest – props Sid Cranstone and Andy Mortimore and the two flankers, Karl Brown and Richard Turnbull.
Unbeaten in the league, Farnham have now reached the third round of the cup for the first time in their history.
The club were also celebrating wins across the board on Saturday.