Back at the site of his junior triumph two years ago, the 19-year-old Jodar looked unusually out of sorts after his first-round clash was delayed by a day due to rain, with a flurry of unforced errors handing Bu the opening set.
Things looked to be going from bad to worse for Jodar when Bu, the last-minute beneficiary of a spot in the main draw after Thanasi Kokkinakis withdrew, broke early in the second set and threatened to run away with the contest.
"I'm a really lucky loser," Bu said.
"After I lost in qualifying, I took a day off but I saw a few guys pull out, so I took the decision to come back and tried to do some work in case I could play. Yesterday, they told me I could ... when I heard that, I was super excited."
Jodar, one of the fastest-rising talents in the men's game after going from 362nd in the world to 13th over the past year, continued to struggle for answers and even sent several of his rackets to be re-strung in a bid to change his fortunes.
But it proved futile, with the 24-year-old Bu refusing to loosen his grip on the contest as he sealed the second set after another unforced error from Jodar to silence a vocal contingent of Spanish supporters on Court 17.
World number 124 Bu completed the upset after an hour-long rain delay, securing his maiden Grand Slam main-draw victory on his seventh attempt and setting up a second-round clash with Fabian Marozsan or Michael Zheng.
"It was a little bit hard with the rain delay," Bu said.
"We just had to do our job and stay focused. I'm really happy for that. It may have looked very easy, but in my mind and my heart there were lots of emotions. I was very nervous."
