Evans had entered the tournament as a lucky loser following Radek Stepanek's withdrawal and produced a huge shock to reach his first tour semi-final after beating Germany's Philipp Kohlschreiber.
However, the 23-year-old from Birmingham was unable to see off the challenge of the experienced Haas, with the German coming through in a time of one hour and 58 minutes.
With the first set evenly poised at 5-5, Evans made a vital break of serve before holding his own to take the first set.
The second set then went with serve until Haas claimed the crucial break to level the match at one set apiece, taking it 6-4 to set up a decider.
The 35-year-old won what turned out to be the solitary break of serve in the third and final set to move into a 4-2 lead, before closing it out to win the match 5-7 6-4 6-3.
Haas will face fifth seed Marin Cilic in the final, after he defeated qualifier Bjorn Phau 6-3 6-4 in the other semi-final.