The Spaniard has had an injury-hit season, with victories in Melbourne, Doha, Tokyo, and last weekend in Vienna. 

The world number three is finishing the year on a high and has Sunday's final before the ATP Finals in Turin start next weekend. 

"I'm really happy and proud of myself," Alcaraz said. 

"This tournament has always been really tough for me. I've struggled every time I come here. The farthest I have gone [before] was the quarter-finals," he continued.

"I've come into this part of the season much fresher, hungry, ambitious, excited about coming to the tournaments and stepping on the court, playing matches and competing. I'm just really happy that I made the final."

American third seed Shelton dispatched home hope Luca Van Assche 5-7, 6-3, 6-4.