McHale was leading Zarina Diyas, 6-2, 3-1, when the Kazakhstani had to retire with a hamstring strain.
"I don't think the score shows how close the match was up until then," McHale said. "It's a shame she got injured and couldn't keep playing because the games were pretty close. All the games were close. I was playing well and serving well, and I'm happy I was able to win most of those close games.
"I wasn't expecting her to pull out. I hope she recovers quickly from this."
McHale kept laying on the praise for Diyas in her post-match interview.
"I think she's playing really well these days. Obviously she had two really good wins here. She takes the ball really early and hits the ball really flat, so you really need to prepare early on both sides."
McHale isn't through to her first WTA semifinal, but it will be her first WTA semifinal on clay.
"I'm really excited to be in the semis," she said. "I've played here a couple of times but this is the first time I've made the semis, so it's really exciting for me. I hope to play well again tomorrow.
"I'm just thinking about tomorrow's match first. I'm feeling ready."
McHale and Soler-Espinosa will be playing against each other for the first time.
The other semifinal will pit Keys against another WTA rising star, Monica Puig, after the Puerto Rican surprised the only seed left in the tournament, No.4 seed Andrea Petkovic, by a 6-4, 6-4 scoreline. Keys had won a see-saw three-setter against Julia Goerges earlier on in the day, 6-2, 2-6, 6-2.
"She has a great forehand, so I was definitely trying to stay away from that," Keys said of Goerges. "So I was just trying to play my game, play to her backhand more, and wait for the right opportunity.
"She had played almost every US player in the draw. Other than Christina she had played the entire US Fed Cup team. So I talked to Sloane and Lauren before the match - I was very well prepared for it!"
All four semifinalists will be seeking their maiden WTA title at the Internationaux de Strasbourg over the next two days. In fact only one of the final four - McHale - has even been to a WTA final before, finishing runner-up at Acapulco earlier this year (to Dominika Cibulkova). Soler-Espinosa is trying to reach her first WTA final, Keys is trying to do the same, and Puig is in her first WTA semifinal.