Washington - Ivo Karlovic, seeking back-to-back titles on different surfaces at age 37, advanced to the ATP and WTA Washington Open finals on Saturday by defeating US fifth seed Steve Johnson 6-4, 6-4.
The 35th-ranked Croatian blasted 14 aces to reach Sunday's championship match as on-court temperatures cracked 140 degrees Fahrenheit (60 Celsius), well above the hardcourt thermometer's usual upper limit.
Karlovic, who won his seventh career ATP title last week on Newport grass to become the oldest tour singles champion since 1979, will play Sunday's final against the winner of a later match between seventh-seeded German 19-year-old Alexander Zverev and French second seed Gael Monfils.
"It was really hot," Karlovic said. "And also last week was a really different, court and everything. I didn't know if I would be able to adjust. All I can do is be really happy right now.
"I'm not as old as my age suggests."
Karlovic, who averaged 22 aces in his first three wins at the US capital, has not surrendered a service break this week.
"This is my game. This is my strength," Karlovic said of his serve. "I've got to use my opportunities to do what I do best. It is really working this week."
Karlovic rode an early break to claim the first set in 38 minutes, ending it with back-to-back aces, and survived a break point in the second game of the second set when Johnson sent a backhand wide.
In the next game, Karlovic rocketed a service return forehand winner past Johnson and then dropped a slice backhand winner on the line to break for a 2-1 lead. Karlovic faced two break points in the fourth game but answered with three aces and a service winner to hold and went on to win in 78 minutes.
Johnson, ranked a career-high 25th after taking his first ATP title last month at Nottingham, had won three of four prior matches with Karlovic, including a third-rounder at Washington in 2014.
Karlovic, 7-8 in ATP finals, is 2-2 in ATP matches against Monfils, losing their most recent meeting at Madrid in 2011, and beat Zverev at Halle last month in their only meeting.
Zverev, Washington's youngest semi-finalist since Juan Martin del Potro won in 2008 at age 19, could become the first teen ATP champion since Marin Cilic won the 2008 New Haven crown at 19.
Monfils, ranked 17th, is 2-0 versus Zverev, including a February quarter-final win at Rotterdam, as each seeks his third ATP final of the year.
Zverev, ranked a career-high 27th, is the youngest player in the top 30 since Rafael Nadal in 2005 after reaching his first two ATP finals in Halle and Nice over the past two months.
Monfils, 29, seeks a sixth career title, his first since 2014 in Montpellier, as well as his first title outside of Europe and first outdoor crown since Sopot in 2005. His 5-19 ATP finals record includes a 2011 at Washington to Radek Stepanek.
Belgian seventh seed Yanina Wickmayer and Kazakh sixth seed Yulia Putintseva will meet in a later women's semi-final with the winner to face an American, either 122nd-ranked Lauren Davis or 173rd-rated Jessica Pegula, in Sunday's final.
Wickmayer seeks her fifth WTA title, her first since last year at Tokyo, while the others are in their first tour semi-finals.