Head coach David Ripley admitted it was one that got away for the Steelbacks after they suffered a two-run defeat at home to Birmingham Bears on Tuesday night.
Ripley's men couldn't quite chase down the Bears' 172 for nine, in which Richard Gleeson and Rob Keogh both took two for 27 and Rory Kleinveldt claimed one for 20.
Richard Levi (33) and Adam Rossington (43) did get the Steelbacks off to a flyer in reply, with the NatWest T20 Blast champions reaching 51 without loss in just four overs.
But Jeetan Patel (2-27) turned the screw and Aaron Thomason held his nerve in the final over to run out Alex Wakely, who had made a fine 52, from the last ball of the match.
The victory sent the Bears top of the North Group, while the Steelbacks missed the chance to hit the summit and remain fourth ahead of Thursday's home game against Lancashire Lightning.
"I don't think it was a bad performance," Ripley said.
"We did a lot of good things, it's just that when it's so close, it's a tough call.
"We've been winning those games and when you lose one it hits you hard.
"Our performance in terms of restricting them to what we thought was a par score and being in a position to win the game was good.
"We came out of the powerplay well and this was a night where we felt we should win, but this is a night we haven't won and that's disappointing.
"They fought back, they took wickets at key times.
"Losing Adam (Rossington), who was well set, and then Ben (Duckett) next ball was a bit of a dent, but we got so far ahead of the rate, I still felt we would get home.
"But to be fair, they kept fighting, they squeezed us and we just couldn't quite get over the line."