Settling in the second half of the pack, Ocean Park made a long, sustained run to put himself into the race at the 400m.
In search of a fourth successive Group One triumph, Ocean Park levelled up to All Too Hard at 100m before edging ahead.
"It's the epitome of every trainer's career," Ocean Park's trainer Gary Hennessy said.
The Gai Waterhouse-trained Pierro finished third, just ahead of Ethiopia.
Modern-day great Makybe Diva gave Boss his breakthrough Cox Plate win and he partnered So You Think in the first of the horse's two victories in the race.
Damien Oliver says his spring racing carnival is alive again after he won the prized ride aboard 2010 Melbourne Cup winner Americain.
The owners of the French-trained galloper who will be lining up for his third Melbourne Cup, sacked regular jockey Gerald Mosse, replacing him with Oliver. "It's given me a huge lift," Oliver said. "It's been pretty difficult up until now to get really into it."
Oliver lost the Cox Plate mount on Green Moon and was replaced on Caulfield Cup fifth placegetter My Quest For Peace.
Oliver's dumping followed an allegation, so far undenied, that he placed a $10,000 bet on a rival horse in a race in which he rode at Moonee Valley two years ago. The allegation is the subject of a stewards' inquiry.
Mosse's handling of Americain had come in for criticism more than once, but his Caulfield Cup performance is understood to have tipped the balance against him.
The Frenchman has ridden with outstanding success in Europe and Hong Kong, but some of his efforts in Australia, including his handling of Elegant Fashion in the 2004 Cox Plate, have raised eyebrows.
