Voters in harness racing’s Greatest Of All Time Challenge are hot to trot.

Translation: champion trotters Muscle Hill, Mack Lobell and Moni Maker advanced through three rounds each and into this week’s Final Four. Niatross is the only pacer remaining in the month-long contest that allows fans to vote via twitter from Wednesday until 9 a.m. EST Friday each week.

Muscle Hill was a runaway winner over 2019 Horse of the Year Shartin N in last week’s Elite Eight round, earning 79 percent of the vote. Mack Lobell edged Nihilator, the sport’s first $3 million earner, by a 53-47 percent vote. They will meet in one semifinal of the contest sponsored by Omega Alpha and U.S. Trotting Association FanZone.

Though they raced in different decades, they share some similarities. Muscle Hill was unbeaten as a 3-year-old in 2009, winning the Hambletonian by 6 lengths and earning $2.46 million that season, the most by a trotter or pacer. Mack Lobell won the Hambletonian by 6-1/4 lengths in 1988 and set world records along the way to winning his first of two Breeders Crown trophies. Muscle Hill won 20 of 21 races, with all his wins by at least one length. Mack Lobell won 39 races in the U.S. and stakes races in five countries after he was sold as a 4-year-old.

Moni Maker, who will meet Niatross in the other semifinal, also had worldwide appeal. She was the first American-based trotter to win the Prix d’Amerique and Prix de France and won the Elitloppet in Sweden at age 5 in a world-record 1:53.3. The 2-time Horse of the Year won 67 times and earned $5.59 million.

Niatross topped $600,000 in earnings during a 13-for-13 freshman season, the most by any 2-year-old in 1979. The following year, he won the Meadowlands Pace, the first $1 million horse race ever. He broke six records in winning back-to-back heats in the Little Brown Jug in 1:55 and 1:54.4 en route to the Pacing Triple Crown.