The first Thoroughbred meet in Saratoga took place in August of 1863, on the site of the old trotting course, across Union Avenue from the current track. Known as Horse Haven, just south of the Oklahoma, portions of the old track still exist (pictured below), though parts of it have been paved over and it’s no longer used for training or racing.

The first meet ran from August 3rd to 6th and featured two races a day, though, as Ed Hotaling explains in his comprehensive They’re Off! Horse Racing at Saratoga,

There would be two races a day, starting with a best-of-three one-mile heats,
followed by a two-mile dash. It would be misleading to say there were “only” two
races daily, as each day’s heats and longer dashes equaled a five-race card
today. And what the animals went through is hard to imagine today, when a mile
and a quarter is a major test. A nine-mile race—three heats of three miles
each—was still common then.

Though a financial success for John Morrissey, the meet’s organizer and the man to whom Thoroughbred racing can be traced in New York, the physical set-up for the races was less than desirable. There was nowhere to sit and poor sightlines for the track; the turns on the track were “ridiculously sharp.”

As a result of these imperfections and the profitability of the meet, John Morrissey called for subscriptions to set up a jockey club and build a new track. Supported by the social and industrial elite, the Saratoga Association pulled in the thousands of dollars necessary to purchase the land that is the site of the current track, and the men who led this project are among those whose names are recorded in racing history: William R. Travers, Leonard Jerome, and “Commodore” Cornelius Vanderbilt.

A year after this first meet, Thoroughbred racing in Saratoga as we know it was born. On opening day of 1864, August 3rd, Kentucky won the first “Traverse” stakes, for three year olds carrying 100 pounds, at one and three-quarter miles (New York Times). Several days before the meet, the Times previewed it:

The first meeting over the new race-court commences to-morrow (Tuesday). The course is admirably arranged, and thanks to a genial rain, in fine condition for
racing purposes. The liberal character of the numerous stakes and purses each
day of the five to which the season extends, has attracted all the best racing
stock from all parts of the Union…The Grand Stand is admirably located, and a
model of comfort and convenience, and no effort will be spared to render the
meeting a most brilliant one. Saratoga is already crowded with visitors, in
anticipation of this racing carnival, and each hour adds to their number.

I’m not sure that I’d characterize the rain that I’ve seen each day since my arrival as “genial,” but given how dry it’s been here, perhaps the rain, genial or otherwise, is contributing to the courses being in “fine condition” for racing today. The “admirably located” Grand Stand is the same one that stands today. Again, Hotaling:

On that day in August, the carriage riders turned right into the nation’s first
modern sports facility, which, astoundingly, survives today as the oldest major
sports facility on the continent and one of the oldest in the world. Surrounded
by a ten-foot fence, it looked very much in 1864 as it does today if one forgets
the current clubhouse and a few other additions.

No horse today will run longer than a mile and a sixteenth, and this year’s renewal of the “Traverse” stakes is still weeks away, but the 90th running of the Schuylerville, for two year old fillies, will root opening day firmly in its historic past. Those of us who venture towards the course on Union Avenue this afternoon will be no less eager (though perhaps a little more casually dressed) than those who did so 144 years ago, when, in the midst of the Civil War, the resort town in upstate New York gave birth to the meet that we so enthusiastically anticipate each year.

Hotaling, Edward. They’re Off! Horse Racing at Saratoga. Syracuse: Syracuse University Press, 1995.