Eventful contest settled by goals from Italian strike duo to earn Friuli another crack at Europe's premier cup competition next season
Guidolin's men were quick out of the blocks and took the lead through talisman Antonio Di Natale's lovely 18th minute strike. Hosts Catania were awarded a lifeline before the break, but saw Argentine forward Alejandro Gomez screw his penalty wide. Udinese made sure of the three points on the hour, Diego Fabbrini slotting home after a slaloming run.
The Friuli, who lost to Arsenal in the Champions League qualifiers earlier this season, will now have their eyes firmly on reaching the group stages next time round.
Both sides started the contest sharply - Catania looking to play, but finding themselves under early pressure.
Udinese could have been one up within 30 seconds, Di Natale racing clean through on Juan Carrizo in the host's goal - only for the 34-year-old to uncharacteristically drag his shot wide.
Catania entered the contest with something of a reputation as draw specialists after sharing the spoils fifteen times prior to the clash. However, the visitors looked hungry to secure their Champions League spot and took the lead just shy of the 20 minute mark through the prolific Di Natale.
Di Natale atoned for his earlier miss, racing onto Maurizio Domizzi's through-ball to score his 23rd of the season with a fantastic dinked finish from an acute angle.
The Elefanti were certainly not out of the contest, but - though lively in attack - they were creating little.
However, the host's persistence paid off on 38 minutes when Friuli midfielder Roberto Peyreyra ill-advisedly dangled out a leg, which Andrea Catellani promptly fell over after minimal contact. Argentine Gomez stepped up to take the spot-kick, but directed a poor effort wide of Samir Handanovic's right-hand post.
Udinese reasserted themselves after the break and calmed their nerves on the hour, Fabbrini finishing off a fine solo run with a firm low finish.
Catania plugged away, sub David Suazo firing wide and Nicolas Spolli drawing a fantastic save out of Handanovic with a header. Suazo should really have clawed one back for the hosts at the death, but was unable to convert Felipe Seymore's cross.
Victory was assured, but Kwadwo Asamoah nearly put further icing on the cake for Udinese - hitting the post for the visitors.
Guidolin's side saw the game out and his delighted troops will now recharge their batteries this summer looking forward to a Champions League qualifier next term. Vincenzo Montella's Catania, meanwhile, will look to build on their creditable mid-table finish this season.