Aljaz Bedene said he struggled to cope with the shock of failing in his bid to play Davis Cup tennis for Britain as he reached round two of the Miami Open.
He beat Spain's Roberto Carballes Baena 4-6 6-2 6-3, 24 hours after being ruled ineligible to represent his adopted nation in the annual team tournament.
"I'm still shocked, to be honest," said the Slovenia-born Bedene, 26.
Britain's Heather Watson beat American Sloane Stephens to reach round three of the women's singles.
Watson won the last 11 games to record a 6-3 6-0 win and will now play Belgium's Yanina Wickmayer.
"My game just all clicked together and I started to play really well," said Watson, who trailed Stephens 3-1 in the first set before beginning her run.
"I was being aggressive and not making many errors. She started to make more errors. I'm very happy with how I stayed there."
While Bedene said he respected the International Tennis Federation ruling, he said he was angry with the way it had treated him.
"Even today, the first set, I was still thinking about it," said the British number two, who next plays Spanish 17th seed Roberto Bautista Agut.
"I've been struggling. I was sad, almost crying. It's been difficult and I really wanted it. I'll still keep fighting."
Bedene is considering taking his case to the Court of Arbitration for Sport but fears it could cost "six figures" and so prove impossible.
"I think the best thing is the lawyers check it and see if there is a chance," said the world number 57, who said he would consult with the Lawn Tennis Association.
"Not a slight chance, but a good chance to win. If not, I don't think it's fair on the LTA to do this."