Set an unlikely 388 to win or a minimum 138 overs to survive for the draw needed to protect their 2-1 lead and regain the trophy held since 1995 by Australia, the West Indies were reduced to 69 for 3 when McGrath went through Brian Lara's defence to secure umpire Dave Orchard's lbw decision.
Occasional medium pacer Greg Blewett gained Orchard's less obviously lbw verdict against Carl Hooper 20 minutes before the close, leaving the home team 105 for 4, 288 behind and the left-handers Jimmy Adams and Adrian Griffith, the last of the specialist batsmen, together.
Their miraculous fightbacks, inspired by Lara's devastating batting that brought them victories in the second and third Tests, now seem beyond the compass of the West Indies.
Lara, whose heavy scoring form has brought him scores of 213 in Kingston, 153 not out in Bridgetown and an 84-ball 100 in the first innings here, went for seven. It was an event greeted by whoops of delight from the Australians on the field and their hundreds of supporters in the stands - and silence by the dumbfounded locals.
McGrath was brought back for a second spell immediately Lara replaced Dave Joseph, out to a reckless stroke to mid-on off medium pacer Adam Dale in the third over after tea.
McGrath collected a bonus wicket second ball. Lara pushed the first away on the leg-side bringing Sherwin Campbell on to strike. The little opener had seen off his threatening opening burst and seemed well set with 29 but, needlessly chasing a wide outswinger, snicked a catch to the tumbling Ian Healy.
Lara spent 40 circumspect minutes over his 26 balls before he trudged off, trapped in front by one that straightened on him.
McGrath had already created a setback for the West Indies in his opening nine overs, cracking Griffith on his right elbow and forcing him to retire for 10. The blow caused swelling, but he resumed when Hooper departed.
Earlier, Australia temporarily lost their way against fast bowling of vintage quality by Curtly Ambrose and Courtney Walsh, well supported by Hooper's containing off-spin.
In a commanding position at the start, 209 for 2 and already 290 ahead, they spent 42.4 overs adding 97 before they were bowled out for 306, their last six wickets falling for 41 runs.
Justin Langer moved from his overnight 84 to 127, his third Test hundred spanning six hours 35 minutes with two sixes and eight fours. But no one could lift the scoring rate or resist Ambrose who finished with 3 for 55 from 27 overs or Walsh, with 4 for 78 from 32.4 overs.
Fourth day of five; Australia won toss
AUSTRALIA - First Innings 303 (S R Waugh 72no, J L Langer 51; C E L Ambrose 5-94).
WEST INDIES - First Innings 222 (B C Lara 100).
AUSTRALIA - Second Innings
(Overnight: 209 for 2)
J L Langer b Hooper 127
M E Waugh c Jacobs b Ambrose 65
*S R Waugh c Jacobs b Ambrose 4
R T Ponting not out 21
I A Healy c Adams b Hooper 16
C R Miller c Lara b Walsh 1
A C Dale c Hooper b Walsh 0
S C G MacGill c Perry b Hooper 2
G D McGrath b Walsh 2
Extras (b2, lb1, w3, nb11) 17
Fall (cont): 3-223, 4-241, 5-265, 6-287, 7-288, 8-288, 9-296.
Bowling: Ambrose 27-10-55-3; Walsh 32.4-6-78-4; Hooper 30.4-7-69-3; Adams 8.2-2-13-0; Collymore 16-1-60-0; Perry 7-0-28-0.
WEST INDIES - Second Innings
A F G Griffith not out 16
S L Campbell c Healey v McGrath 29
D R E Joseph c Miller b Dale 17
*B C Lara lbw b McGrath 7
C L Hooper lbw b Blewett 12
J C Adams not out 18
Extras (lb4, nb2) 6
Total (for 4) 105
Bowling (to date): McGrath 18-8-27-2; Dale 8-3-25-1; MacGill 5-0-21-0; Miller 12-4-24-0; Blewett 4-1-4-1.
Umpires: S A Bucknor (WI) and D L Orchard (SA).Reuse content