Dominic Thiem and David Goffin will be battling in a virtual quarterfinal match at the Nitto ATP World Tour Finals when the friendly, familiar foes square off again on Friday afternoon.

Goffin leads the head-to-head series 6-3 at the ATP level (7-3 overall), including 4-1 on hard courts. Their only completed indoor meeting (not counting one first-set retirement by Goffin) came four years ago in Basel, where the Belgian prevailed 7-6(4), 6-3. They have squared off twice in 2017, with Goffin getting the job done 5-7, 7-6(4), 6-2, 6-2 at the Australian Open and 7-6(4), 4-6, 6-3 at the Monte-Carlo Masters.

The latter marked a rare clay-court loss to someone other than Rafael Nadal for Thiem, who captured the Rio de Janeiro title, placed runner-up to Nadal in Barcelona and Madrid, and reached the Roland Garros semis before falling to the eventual 10-time champion. A woeful second half of the year saw Thiem turn in only a few decent results, one of which was a fourth-round showing at the U.S. Open–but that ended in a collapse against Juan Martin Del Potro from 6-1, 6-2 up.

Goffin’s recent months have progressed in different fashion. His French Open campaign ended abruptly in the form of an ankle injury, but he has been in fine form since his hard-court return. The world No. 8 advanced to the last 16 in New York, won back-to-back titles in Shenzhen and Tokyo, and made a run to the Basel semis.

Goffin has produced a mixed bag so far at the O2 Arena. He beat a hobbled Nadal 7-6(5), 6-7(4), 6-4 only to get thrashed by Grigor Dimitrov 6-0, 6-2 on Wednesday. Thiem’s two-year history at the year-end championship has been solid. He went 1-2 last year, with a win over Gael Monfils and a three-set loss to Novak Djokovic among his results, and is 1-1 through two matches this week (lost to Dimitrov 6-3, 5-7, 7-5; beat Pablo Carreno Busta 6-3, 3-6, 6-4).

“I practice really often with Dominic,” Goffin commented. “I have already an idea with the tactics against him because I played so many times against him. We played a lot of good matches against each other. It’s not going to be easy.”

“I’m very happy and pleased that I get the chance to play for the semifinals on Friday,” Thiem assured. “Not much calculating. The winner [goes] through. We had some big, important matches in the past…in the deep rounds of slams. This one’s going to be another one. We know each other very well. He played a very good match here (against Nadal); one very bad match (against Dimitrov). I don’t know what to expect.”

Not only has Goffin’s form been erratic this week, but he is also a question mark from a physical perspective. Although the seventh seed insists that he is–or is close to–100 percent, he may not have been moving at his absolute best against Dimitrov. If Thiem can play a smart match and choose the correct times to unleash his one-handed backhand, he should advance to the semis.