Jack Sock has become more a doubles contender than singles player in recent seasons. (Getty Images)

Jack Sock was ranked as high as world No. 8 in November of 2017. That was the year he won the Paris ATP Masters and qualified for the ATP Finals. After that breakthrough, the American somehow slid all the way out of the ATP rankings. 

That's not to say that the 27-year-old hasn't been posting big results: he was dominant in doubles in 2018. That season, he won Indian Wells, Wimbledon, the US Open and the ATP Finals. But even that streak seems to have slowed down, for now. 

The 2019 season was one of his worst seasons, losing in the first round of every tournament he played in—although, to be fair, he only played in nine as he dealt with a right thumb injury.

It looks like things are turning around quickly for him. Last month in Delray, Sock picked up his first win, returning him to the singles rankings at No. 768.

He's building on that momentum, stringing together wins at the Oracle Challenger Series in Indian Wells where he's into the quarterfinals with upsets of No. 1 seed Ugo Humbert and No. 13 seed Evgeny Donskoy. How high will the talented American with the signature whip forehand go in his comeback?