Sousa had been due to enter the qualifiers for next week's China Open in Beijing but his continued success on the Malaysian hard courts forced his withdrawal as he goes in search of a first title.
The 24-year-old beat Austrian Melzer 6-4 3-6 6-4 in the last four clash to set up a final on Sunday against fifth seed Julien Benneteau who upset second seed Stanislas Wawrinka 6-4 6-3 in the other last four clash.
"It's going to be tough... I'm going to give 100 per cent tomorrow to win the title here, for sure," Sousa told the ATP Tour. "(If I win) it will be good not just for me, but for my country, Portugal.
"It's a great week for me this week."
The right hander has enjoyed an impressive run at the $875,500 event in Malaysia, knocking out top seed and world number four David Ferrer in the last eight after an opening round win against American wildcard Ryan Harrison.
It comes on the back of reaching his first ATP Tour semi-final in St. Petersburg, Russia, last week which helped him to jump to his career best ranking of 77.
The last Portuguese to reach an ATP Tour final was Frederico Gil over three years ago.
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- ATP Tour