Roger Federer is in action at Halle this week as the Swiss legend puts the finishing touches to his assault on an eighth Wimbledon title.
Federer, who made his comeback after skipping the entire clay court season at Stuttgart last week, faces Lu Yen-hsun, Taiwan's world number 73 on Tuesday.
The ring-rusty 18-time Grand slam winner was knocked out early in Stuttgart by 39-year-old Tommy Haas.
Haas, a former world number two but now down at 252, won 2-6, 7-6 (10/8), 6-4 for just his fourth victory in 17 meetings against his close friend.
It was just the second defeat of 2017 for the 35-year-old Federer, who claimed the Australian Open in January.
Federer, aiming for a ninth title at Halle, has won all three of his match-ups against Lu.
He turns up in the Westfalen town after recharging his batteries at home in Switzerland.
"I've got high hopes of playing better here than in Stuttgart last week," the world number five said, adding that he was "in 100 percent form for the grass season".
Federer followed up his Australian Open triumph with wins at Indian Wells and Miami, before taking a two-and-a-half-month "timeout" to ensure he was fit and fresh for Wimbledon.
If he gets past Lu, Federer could face Mischa Zverev in the second round.
Zverev's 20-year-old younger brother Alexander, German tennis's latest prodigy and world number 12, opens his tournament against Italy's Paolo Lorenzi.
Japan's Kei Nishikori, beaten in the French Open quarter-finals by eventual winner Rafael Nadal, opens against Spaniard Fernando Verdasco.
France's Lucas Pouille arrives in Halle hot foot from his success on the grass at Stuttgart on Sunday where he came from behind to beat Spain's Feliciano Lopez 4-6, 7-6 (7/5), 6-4.
The 23-year-old, who reached the Wimbledon quarter-finals last season, plays local hope Jan-Lennard Struff, the German he beat last week.