Defending champion Grigor Dimitrov eased into round two of the Brisbane International with a hard-fought win over qualifier Yannick Hanfmann on Monday, but Holger Rune crashed to defeat.
Bulgaria's second seed Dimitrov has a great track record in the city, winning the title twice, as well as making the final in 2013.
His 7-6 (7/5), 6-3 victory over Germany's Hanfmann was his 24th in Brisbane, more than any other player.
Yet he has flown under the radar this year due to the presence of former world No 1 Novak Djokovic and the comeback of mercurial Australian Nick Kyrgios.
"I came here 15 years ago and since day one I've had that love affair (with Brisbane), so I want to keep on going, keep on testing myself and delivering as long as I can," Dimitrov said.
"Hopefully I can continue and go all the way again. I enjoy the weather – it's hot and humid and I like that," added the world number 10.
Czech Jiri Lehecka caused a major upset with a 7-5, 6-3 win over third seeded Norwegian Rune.
"To win and begin the season like that is always a good start," the 23-year-old Lehecka said. "The conditions suit me well here."
Earlier, eighth seeded Australian Jordan Thompson came from a set down to overcome former world No 6 Italian Matteo Berrettini 3-6, 6-3, 6-4.
Berrettini is now 34th in the world, only eight places behind Thompson and that closeness showed in a match that last two hours, 15 minutes on Pat Rafter Arena.
"I mean today I think I was eighth seed and playing Berrettini," Thompson said.
"I don't know how he's not seeded. But I feel like everybody could be a seed. This is one of the strongest tournaments of the year."
In other matches, French qualifier Benjamin Bonzi upset sixth seeded Chilean Alejandro Tabilo 6-7 (8/10), 7-6 (7/5), 6-4, while American Alex Michelsen beat Australia's Christopher O'Connell 6-4, 4-6, 7-6 (12/10).
Chile's Nicolas Jarry downed Mariano Navone of Argentina and Japanese qualifier Yoshihito Nishioka beat Frenchman Arthur Rinderknech, both in straight sets.
In the women's draw, Russia's Polina Kudermetova defeated China's Wang Yafan 6-1, 6-3.
However, the Russian's older sister Veronika was knocked out by American Payton Stearns 6-2, 6-3.
Ukraine's Anhelina Kalinina progressed when her Chinese opponent Wang Xinyu retired hurt with Kalinina leading 6-4, 2-0.
In an all Australian battle, wildcard Kimberly Birrell outlasted training partner Priscilla Hon 3-6, 7-5, 6-2.