The Dutchman recorded an impressive 6-2, 6-3 win over Sousa to advance to the round if 16 where he will face Liam Broady.
Thiem got off to a good start at the ATP 250 competition as he beat a spirited Laslo Djere 5-7, 7-6(3), 6-4 in the first round.
Novak Djokovic is the standout attraction in the field. He has been off the tour since winning his 21st Major title at Wimbledon.