The 24-year-old saw off last year's semi-finalist Gary Wilson in the third round, before a tense 10-8 victory over Andrew Higginson saw him earn his Crucible debut.
Ursenbacher led 6-2 and 9-6 but had to dig deep to fend off a fightback from Higginson, eventually prevailing by taking the 18th frame courtesy of a re-spotted black.
A break of 96 helped Alan McManus to seal a 10-6 victory over Louis Heathcote, a match in which neither man showed their best.
Kurt Maflin was the first man to earn a Crucible place, thrashing Matthew Selt 10-1, with a 103 break the highlight of an exceptional display.
The Norwegian has played in the World Championship once before, losing 10-9 to then defending champion Mark Selby in 2015.
"I’ll beat him this time!” the 36-year-old said of a potential rematch. "I’m just looking forward to getting back there now and I really enjoyed it last time – obviously the conditions now because of Covid means it’s going to be a bit different, but I’m really looking forward to it now.
"I’ve put a lot of hard work in over the last five or six weeks and it’s looking like it’s paying off.
"I’ve been quite close – last year I think [Graeme] Dott did me in the last round, so I really wanted to get back there this year."
A 141 break in the final frame helped Liang Wenbo scrap passed Fergal O'Brien 10-9, while Anthony Hamilton will return to Sheffield after a 10-5 victory over Scott Donaldson.
Ashley Carty beat Robert Milkins 10-8 despite two century breaks from the latter, who had earlier beaten Jimmy White.
Eliot Slessor also progressed, a 111 break sealing a comprehensive 10-3 victory over Martin O'Donnell.
- Live snooker returns to Eurosport and the Eurosport app. Watch the World Championship and qualifying from July 21 to August 16
Round four results and draw
Monday July 27
- Alexander Ursenbacher 10-8 Andrew Higginson
- Martin O'Donnell 3-10 Elliot Slessor
- Noppon Saengkham 10-2 Eden Sharav
- Anthony Hamilton 10-5 Scott Donaldson
- Ashley Carty 10-8 Robert Milkins
- Matthew Selt 1-10 Kurt Maflin
- Fergal O'Brien 9-10 Liang Wenbo
- Alan McManus 10-5 Louis Heathcote
Tuesday July 28
- Jamie Clarke v Sunny Akani
- Jordan Brown v Ryan Day
- Stuart Carrington v Tom Ford
- Mark King v Ian Burns
- Graeme Dott v Martin Gould
- Matthew Stevens v Ricky Walden
- Anthony McGill v Sam Baird
- Liam Hghfield v Thepchaiya Un-Nooh
All winners enter first round draw at World Championship
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