Also right up there is Sunderland (H) 3-1 AET in the Milk Cup in 1985 which also, spookily enough led to a 5-4 aggregate victory

One of the great nights.
That was a memorable game, along with the win in the next round against Sheffield Wed 1-0, who were 3rd in the old first div (Prem now), and had ben Man U a few days earlier.
Of course in the late 80's we had some great cup games at the CG. Here are a few of them :
Swindon 3 Pompey 1 LC '87
Swindon 4 Chelsea 0 Simod Cup '88
Swindon 2 Norwich 0 Simod Cup '88
Swindon 3 Bolton 3 LC '89
Swindon 2 Bolton 1 AET LC '89
Swindon 4 Norwich 1 Simod Cup '90
Great league games at the CG :
Swindon 4 Chester 2 '86
Swindon 6 Stoke 0 '89
Swindon 4 Blackburn 3 '89
Swindon 3 Lids 2 '90
Swindon 5 Leicester 2 '91
Swindon 5 Sunderland 3 '91
Swindon 4 Cambridge 1 '92
Swindon 1 QPR 0 '92
Swindon 6 Huddersfield 0 '96
Swindon 1 Pox 0 '96 (The Joey Wingebag return game)
Swindon 2 Man City 0 '96
Swindon 3 Brum 1 '97
Swindon 2 Huddersfield 0 '00
Swindon 2 Peterborough 1 '01
Swindon 3 Barnsley 1 '02
Swindon 5 Notts County 0 '03
Swindon 4 Notts County 0 '03