Glamorgan now know that any further defeats could seriously damage their hopes of reaching the last eight.
Kellaway, however, remains confident they can respond when they host table-toppers Northamptonshire on Wednesday.
Fourth-placed Glamorgan trail Gloucestershire and Worcestershire – who are second and third respectively – by four points in the table, but have played one game fewer than both those sides.
The top two teams in each of the T20 Blast’s three groups go into the quarter-finals along with the two others with the most points.
“It’s getting to that stage of the tournament now where every game feels like a knockout game,” he said.
“We’ve got to look past Sunday now and we’ve got three more big games that we need to win, so that’s the simple way of looking at it.”
Northamptonshire are top of the group despite suffering their first Blast defeat of the season against Somerset on Sunday.
Kellaway expects another tough test but is hopeful Sunday’s setback will not derail the momentum Glamorgan had built through three successive victories.
“Momentum in T20 cricket is huge,” he said. “Losses can also be followed by one another when these games come quick and fast.
“We’ve got to really spin it around. We’ve got a training session on Tuesday to re-sort things and then come out fighting on Wednesday.”