Jung recorded his fifth career ATP tour-level win in defeating the 21-year old American, who accepted a wild card into the event at the last minute. Tiafoe was playing in his first tournament since reaching the Australian Open quarterfinals.
Jung takes first set in a surprise
Jung got off to a fast start as he held to 30 and on Tiafoe's first service game of the match, was ahead 0-40. A powerful backhand by the 21-year old forced a wild error from the American to give Jung a 2-0 lead. A solid hold gave the Taiwanese a 3-0 advantage.
Unable to make any impression on Jung's serve so far, Tiafoe fell behind 4-1 and was trailing 0-30 on his own serve before scraping out a hold, but it was still the world number 143 who was in control and after a clever drop shot brought up two set points, a Tiafoe missed forehand put the underdog in front.
World number 143 completes stunner in straight sets
Each man recorded a pair of comfortable holds until Jung had a pair of break points in the fifth game, but was unable to convert. Given two more opportunities in the next Tiafoe service game, the world number 143 converted at the first time of asking with a brilliant running forehand.
Jung held for a 5-3 lead and looked poised to complete the upset holding a match point, but a forehand long allowed Tiafoe to escape. The American finally had a look on Jung's serve and broke back when the Taiwanese double-faulted.
The momentum was short-lived as Jung held a break point and after Tiafoe blasted a forehand over the baseline, the world number 143 broke for a 6-5 edge. Given a second chance to serve the match out, the Taiwanese held to love for a memorable and career-defining victory.