All of the top 10 seeded women have reached the third round at the Australian Open for the first time since 2007.
Pliskova, who defeated 23-time Grand Slam champion Serena Williams en route to her first semifinal in Melbourne 12 months ago, overcame a slow start against Siegemund and advanced after 86 minutes at the Rod Laver Arena.
The world number one was a little profligate with his break points - converting only three of 20 - but still comfortably moved through to a meeting with compatriot Pablo Carreno Busta.
But the initiative it requires to win factors versus Medvedev ultimately took its toll on theSpaniard Serving at 5-6, a worn out Martinez missed out on a set of regular forehands to offer the 4th seed a very early lead.
Looking fluent throughout the match, Popyrin hit as many as 51 winners and broke his opponent four times in the match.
But things suddenly went awry for him when back-to-back double faults put the set back on service before another error set up a break for the Frenchman to win the third set. He knows how to win matches ... "I messed it up", he said. I thought I lifted in the fourth. "I told myself ... just get to work", he added.
Germany seventh seed Alexander Zverev, who has yet to go beyond the fourth round in Australia, beat Belarusian Egor Gerasimov 7-6 (7-5) 6-4 7-5.
Thiem entered the match strongly and won the first set with great ease 6-2, but Bolt shocked him in the second and third by winning them 7-5 and 7-6 (7-5), before the Austrian rose up in the last two groups and won them 6-1 and 6-2, respectively, thus the match In three hours and 22 minutes.
Zverev, the Georgian Nikoloz Basilashvili, or Spaniard Fernando Verdasco, will meet for the final price tag, which he once reached in Melbourne a year ago without succeeding in overcoming it.
Alex Bolt looked to have No.5 seed Dominic Thiem on the ropes when he curled a remarkable forehand victor around the net en route to a two-sets-to-one lead.
Thiem, who has never gone past the fourth round in six previous attempts, ultimately came through to set up another tricky clash in the third round, against either American 29th seed Taylor Fritz or big-serving South African Kevin Anderson.
Following one of Bolt's serves, Thiem's sliced return was near-perfect, landing right near the net, forcing Bolt to charge towards the net before hitting a forehand victor around the post holding the net up.