His first tournament cash came in October 2012, when he took 2nd place at the World Series of Poker Circuit main event in Hammond, Indiana, for $239,063. In the following few months he had several cashes in smaller events throughout the United States. Riess first played the WSOP in 2013, cashing in 3 preliminary events with a best finish of 11th in a $1,000 No Limit Hold'em event. Playing in his first WSOP Main Event, he made the November Nine in 5th chip position with 25,875,000. After eliminating 4 players at the final table, Riess entered heads-up against Jay Farber with a nearly 20 million chip deficit. After 90 hands of heads-up play, Riess' A♥K♥ defeated Farber's Q♠5♠ to win the championship bracelet and $8,361,570.
As of 2014, Riess's total live tournament winnings exceed $8,700,000 of which $8,661,668 have come from cashes at the WSOP.