Melbourne - Andy Murray and Roger Federer are both facing unknown quantities as they bid to reach the Australian Open's third round on Wednesday.
Top-ranked Murray plays Russian world number 156 Andrey Rublev for the first time, as the five-time runner-up sets his sights on finally lifting the trophy.
It shouldn't be a difficult task against Rublev, who won his maiden Grand Slam match against Lu Yen-Hsun in the first round and is yet to win back-to-back matches at tour level.
Murray, by contrast, is looking for his 178th Grand Slam match win, an achievement that would put him alongside Stefan Edberg in eighth place on the Open-era list.
"I've never hit with him or played against him, but I've seen him play before and he goes for it. He doesn't hold back," Murray said.
"When you get out there, things look a little bit different than they might on the TV or on the video. But I'll try to watch... and hopefully go in with a good strategy. I'll need to work some things out myself when I'm out there."
Federer, 35, has a similar situation against America's Noah Rubin, and the Swiss maestro admitted he knew "almost nothing" about the 20-year-old world number 200.
"Did he play here last year? Did he qualify?" Federer asked.
"I know he's a baseliner. He makes a lot of shots. I guess it's not a bad thing for me. I know it's probably more on my racquet rather than playing a big server."
Although Federer can expect only a light work-out from Rubin, victory would potentially pitch him into a difficult third-round match against Czech 10th seed Tomas Berdych.
In the women's draw, world number one and defending champion Angelique Kerber takes on fellow German Carina Witthoeft after a shaky first-up win over Lesia Tsurenko.
Kerber has never dropped a set against the 89th-ranked Witthoeft, beating her at Wimbledon in 2015 and 2016.
"I think it will be a good match. But for me it's important to go out there playing my match again, not thinking too much about my opponent," Kerber said.
Elsewhere Canada's Eugenie Bouchard will be out to extend her recent revival in fortunes when she takes on China's Peng Shuai.
Other day three highlights of the men's draw include Kei Nishikori's clash with Jeremy Chardy, and 2014 winner Stan Wawrinka's match with Steve Johnson.
Bernard Tomic leads home hopes against Victor Estrello Burgos but Australian fans will also cheer teenage wildcard Alex De Minaur, who takes on seasoned American Sam Querrey.