Washington - World No 3 Alexander Zverev spent years playing his older brother Mischa in backyard childhood tennis matches and lost most of the time.
Now the Zverev brothers are both ATP players and after five years together on the tour will meet for the first time in an ATP singles match on Thursday at the Washington Open.
"It's going to be very interesting for me. It will be a special day," Alex Zverev said.
"Not many families can say they have two players playing at this level."
Defending champion Alexander, 21, ousted Tunisia's Malek Jaziri 6-2, 6-1 while Mischa, who turns 31 later this month, beat American Tim Smyczek 6-2, 7-6 (9/7) to book the third-round affair.
"We both wanted to win and play each other," Alex Zverev said. "It's a little bit early in the draw. We're both very excited and we both want to win.
"When we would play (as children) he was trying to beat me 6-0, 6-1. I hope it's not going to be like that tomorrow."
Their careers are a testimony to father Alex Sr., a former ATP player who moved the family from Moscow to Germany in 1991. He coaches both his sons. Mischa played his first ATP match in 2006 when Alex was nine.
"We played the final of Wimbledon a lot of times in our backyard," Alex said.
"I was 12. He was 22. I don't think I ever won. But this is on hardcourt."
Alexander credits his quick development to a top-three ATP player to his time as a junior training against his older brother.
"I don't think many other junior kids had an ATP player to practice against and help with their game," Alex said. "That gave me a big advantage."
Alex Zverev worked with retired star Ivan Lendl for three days in Florida between Wimbledon and Washington in what is for now at least a one-off instructional session.
Mischa Zverev is married, expecting a child and no longer hangs out with his brother as much as before.
"He bought himself a new apartment in Monaco. He's expecting a child in a few weeks," Alex said. "We've gone our separate ways but we're still pretty close.
"It's definitely not just another match for us. We still play doubles together and we will prepare for it the best we both can."
Results on Wednesday from the third day of the ATP and WTA Washington Open (x denotes seeding):
Denis Kudla (USA) bt Karen Khachanov (RUS x12) 6-2, 6-3
Frances Tiafoe (USA x13) bt Hubert Hurkacz (POL) 6-2, 6-4
Marius Copil (ROM) bt Jeremy Chardy (FRA x14) 6-4, 6-4
James Duckworth (AUS) bt Jason Kubler (AUS) 1-6, 6-2, 7-6 (7/5)
Mischa Zverev (GER x15) bt Tim Smyczek (USA) 6-2, 7-6 (9/7)
Denis Shapovalov (CAN x9) bt Daniil Medvedev (RUS) 3-6, 6-1, 6-4
Stefanos Tsitsipas (GRE x10) bt Jared Donaldson (USA) 3-6, 6-3, 7-5
Lucas Pouille (FRA x6) bt Vincent Millot (FRA) 6-7 (2/7), 6-4, 3-0, retired
Andy Murray (GBR) bt Kyle Edmund (GBR x4) 7-6 (7/4), 1-6, 6-4
Alexander Zverev (GER x3) bt Malek Jaziri (TUN) 6-2, 6-1
David Goffin (BEL x3) bt Pierre-Hughes Herbert (FRA) 6-2, 1-6, 7-6 (7/5)
Chung Hyeon (KOR x8) bt Marcos Baghdatis (CYP) 6-7 (2/7), 6-4, 6-3
Kei Nishikori (JPN x7) bt Donald Young (USA) 6-3, 6-4
Tommy Paul (USA) bt Alex Bolt (AUS) 3-6, 7-6 (7/0), 6-2
Andrea Petkovic (GER) bt Sloane Stephens (USA x2) 2-6, 6-4, 6-2
Ysaline Bonaventure (BEL) bt Anhelina Kalinina (UKR) 6-3, 6-3
Zheng Saisai (CHN) bt Katie Swan (GBR) 6-2, 6-4
Jen Brady (USA) bt Natalia Vikhlyantseva (RUS) 6-1, 6-4
Magda Linette (POL) bt Olivia Rogowska (AUS) 6-4, 6-1