Mackenna will be an odds-on favourite to go through to the Ladbrokes Million Dollar Chase final after drawing box one and posting near record time in a trial but last week's Wentworth Park Qualifier winner Jay Is Jay also looks a safe bet in Friday night's semi-finals of the world's richest greyhound race.
Mackenna, who clocked 29.32 in his first look at Wentworth Park, will wear the red rug in the first semi-final and is undefeated in two races from box one.
Jay Is Jay's qualifying time of 29.73 was .17sec outside the best of the night but there wasn't a more impressive winner at Wentworth Park last Saturday night than Selena Zammit's Albion Park 520m record breaker.
Jay Is Jay got onto the heels of the pacemaker going through the first bend and became so unbalanced he looked in danger of taking a tumble.
But he recovered brilliantly and ran down the tearaway leader Flash As Joe to win running away by just under a length.
Jay Is Jay, box two, looks to have a great draw in Friday's third semi as Saige Tenniele, who has box one, was doing her best work at the finish when she trialled 29.66 at Wentworth Park last Saturday.
Jay Is Jay boasts five wins and a placing in six starts from box two.
Pre-post MDC favourite Postman Pat makes his keenly anticipated Wentworth Park debut in semi-final eight of the Chase and goes into the race after a fast 29.60 trial at the track last Saturday night.
Postman Pat, who has had two wins and a placing in three appearances wearing the pink jacket, has box eight on Friday and has had two wins and a placing in three outings from the outside alley.
Caretaker trainer Peter Lagogiane said: "Postman Pat's trainer Jason Thompson told me the dog always improves at his second run on a track.
"Postman Pat's kennelmate Umberto, who has box two in the second semi, has had a box-to-box hit-out at Wentworth Park and recorded a quick first split of 5.39 and a third section of 17.97.''
Lagogiane has his own dog Nad Al Sheba in box seven in the fifth semi-final and believes the dog is good enough to win so long as he "nails the start.''
The hardest for Nad Al Sheba to beat could be Victoria's Yachi Bale, who has box one following a fast finishing photo-finish second to Bandit Bluey in a 29.86 qualifier last Saturday.
"Landyn Bale has terrific pace in the middle stages but tends to get a bit tired in the straight,'' Delbridge said.
"He handles wide boxes pretty well in Melbourne.''
Delbridge revealed his stayer Zoha Bale had trialled 41.86 over 720m at Wentworth Park in preparation for his appearance in Friday night's first heat of the Sydney Cup.
Zoha Bale faces stern opposition from Zipping Kansas (box one), Ritza Piper (two) and Untapped (four).
Ritza Piper, a winner of eight from 16 Wentworth Park 720m outings, is "flying" at present and has just clocked a fast 29.56 in a 520m trial at headquarters.
Veteran Untapped turned four in April but is going as well as ever according to trainer Dustin Drew.
In three races over 720m at Wentworth Park Untapped has had a win and a second and Drew said: "I took her to Warrnambool on Monday and she broke 22sec in a 390m sprint.
"That is fantastic for a stayer because that's what the top-grade sprinters run.''
Drew also has My Catalina in box four in heat two but pointed out that she had never seen Wentworth Park.
"I've only had her for four starts but she is a good bitch and will run out the 720m on her ear.''
Zipping Vanessa will be chasing her sixth win in eight Wentworth Park 720m races in this heat but is also up against Jason Thompson's smart Victorian Triumph (box five) and Queenslander Valpolicella (box seven).
Triumph trialled a slick 29.90 over 520m at Wentworth Park last week while the Tony Zammit-trained Valpolicella, a winner of her past seven starts at Albion Park, clocked 42.08 before trimming those figures to 41.75 in a subsequent Wenty trial.
