How they got here
Thiem was seeded fourth in Acapulco. In the first round, he defeated Bosnian Damir Dzumhur 7-6(3), 6-3. He followed that up with a second round win over Russian Dmitry Tursunov, coming back from injury, 6-7(5), 6-3, 6-4. In the quarterfinals, Thiem knocked off the seventh seed, Bulgarian Grigor Dimitrov 7-5, 6-2.
Querrey came into Acapulco unseeded. He started with a blowout win over Israeli Dudi Sela 6-2, 6-0 in the first round. The following match caused people to take notice: a second-round upset of Japan's Kei Nishikori 6-4, 6-3. In the quarterfinals, Querrey came from behind to defeat fellow American Taylor Fritz 2-6, 6-4, 6-4.
Thiem and Querrey have never played each other before.
What to expect
Both players are on fire. Thiem has won 11 of his last 12 matches, having won the tournament in Buenos Aires, defeating Rafael Nadal and Nicolas Almagro in the semifinals and finals, respectively, getting to the semifinals of Rio De Janeiro, upsetting David Ferrer in the quarterfinals there and now the semifinals here. Querrey has won eight consecutive matches, winning the title in Delray Beach over Rajeev Ram in the final and now three more wins here, including the previously mentioned upset of Nishikori and a come-from-behind effort against Fritz.
It might take a few games for these two to feel each other out as they have never played before. Thiem has separated himself from his fellow generation of youngsters with four titles in the last year and now a top 15 ranking. He has a wonderful all-around game that he'll use in this match against Querrey. For the American, a return to form signals a possible return to the top 30 at some point.
His main weapons of the serve and forehand have been clicking these last two weeks, enabling him to get on this current hot streak. His height and power should enable him to win a few free games on serve. Both players have only dropped one set in the tournament.
Thiem in 3 sets. Although it wouldn't be a surprise to see either player win this match, Thiem is playing at a very high level and he gets the edge based on the quality of his recent wins, beating Nadal, Almagro and Ferrer all on their best surface (clay). Querrey's serve and forehand will test Thiem, especially on this hard court surface, but the Austrian will win a close match and advance to the finals to face either Alexandr Dolgopolov or Bernard Tomic.