Duelling Sydney to Hobart supermaxis Black Jack and LawConnect could be set for a line-honours battle up the River Derwent.
The pair were neck-and-neck down Tasmania's east coast on Tuesday, followed closely by Hong Kong's SHK Scallyway 100 which is considered an outside chance.
Monaco's Black Jack held a seven nautical mile lead at 5pm (AEDT), with LawConnect, a previous winner as Perpetual Loyal in 2016 and Investec Loyal in 2011, in second.
The 100-footers capitalised on strong breezes but will likely have to deal with typically still conditions when they hit Hobart's River Derwent.
Cruising Yacht Club of Australia commodore Noel Cornish said a finish about 2am on Wednesday was expected.
"There is a chance they could be match-racing up the Derwent after two solid days of racing," he said, not ruling out a charge from SHK Scallyway 100.
"Black Jack is lighter and would go better in lighter conditions. LawConnect is a better boat, wider, in the heavier conditions. How that plays out in reality, I don't know.
"Often the Derwent does shut down on breeze ... it often happens around 10pm."
The tightest finish in race history came when Condor of Bermuda pipped Apollo III by seven seconds in 1981.
LawConnect has experienced problems with its position tracker, with its location instead determined through radio reports.
This year's 628-nautical mile event is one of the slower in recent years, a long way behind Comanche's 2017 record of one day, nine hours, 15 minutes and 24 seconds.
Black Jack navigator Alex Nolan said the crew was "pushing hard" in lighter conditions on Tuesday morning.
Rough seas across the first two days have wiped out more than a third of the fleet, with 36 of 88 starting yachts forced to pull the pin.
Rouge Wave, a NSW entrant in the new two-handed category, became the latest to retire on Tuesday after reporting unspecified damage.
Adrienne Cahalan, who has contested 29 Sydney to Hobart events and is the most-capped female sailor, is back in the pack as navigator aboard Oroton Drumfire.
"It's going to be a really big achievement to finish this race, because we've had such a variety of conditions so far," she said.
Quest, Whisper and LCE Old School Racing, all from NSW, are among the handicap frontrunners.
Tasmanian boat Sidewinder is leading the new two-handed category, boats sailed by just two people, ahead of nine remaining competitors.
Two-handed entry Maverick was forced to retire on Monday night after hitting "something heavy".
Co-skipper Rod Smallman said the boat's rudder was damaged and part of the deck was shattered.
"We were taking a bit of water, but there was not a safety issue," he said.
