But a spectacular first-half performance stung Athletic into submission, and they were never able to recover from Slough's opening 20-minute burst, despite a bombardment after the interval during which they hit the woodwork twice and had a goal disallowed.
"We played really well today," said assistant-manager Trevor How afterwards. "It was a good team performance and we coped more effectively with Grays long-ball style than we did last time we met them. Fortunately we seemed to match them for strength today. Grays aren't a particularly nice side to watch, but they're difficult to play against."
How also had a special word of praise for Brian Greenaway, who hit a stunning goal and caused the Blues defence problems all afternoon.
"The supporters are finallv beginning to see the best of Brian. He's taken a while to find his real form, but now he's got a regular place he has settled down."
Greenaway had already swung in a couple of dangerous crosses before he picked out the unmarked Steve Thompson in the 10th minute. Thompson's header took a deflection and looped over keeper Barrie Delf for his 16th goal of the season.
Boosted by an early goal Slough piled forward in search of another goal and it arrived nine minutes later.
Greenaway picked up Keith White's short free-kick and took a few steps before drilling a 25-yard shot beyond Delf and into the bottom corner.
Penned back into their own half, the Blues were unable to make any headway and the Rebels were unlucky not to increase their lead further with efforts from Mark Adams and Greenaway.
Grays introduced substitute Nicky Crown at the start of the second period and his presence immediately perked the visitors up.
Within seconds Gary Dodd was forced to clear Delroy Rhoden's cross off the line and Slough keeper Gary Lester had to pull off a double save from Robbie Garvey as the Blues threatened for the first-time.
Paul Timson then rattled the crossbar and Jimmy Sheringham had a goal ruled out for a foul on Lester in the 61st minute.
But the Rebels managed to survive the onslaught through a mixture of a packed defence and confident goalkeeping, and they should have increased their lead in the 63rd minute.
John Watt's long ball beat Grays' offside trap and Neal Stanley played in the perfect cross for Adams. But the winger failed to keep the ball down and it ballooned high over the open goal.
The Blues must have guessed it wasn't going to be their day when Maverick Bailey smashed a header against the post five minutes later and Rhoden headed the rebound over the empty goal.
Their frustration boiled over and Garwey, Stratford and Ian Brown all picked up bookings before Timson was sent-off in an amazing incident on the stroke of full-time.
Having been cautioned for dissent he then threw a punch at team-mate Stratford as he continued to protest and referee David Keen ordered him off for an early bath.
Grays Athletic Lineup
Delf, Brown, Timson, Fox, Garvey, Stratford, Leslie, Rhoden, Sammons, Bailey, Sheringham. Subs: Crown (for Sammons 45 mins), Hallybone (for Leslie 64 mins).