Smoothly does it for Dibaba and Aman as Vlasic wobbles
Ethiopia's Mohammed Aman (R) crosses the finish line to win ahead of Russia's Stepan Poistogov (L) and Spain's Kevin Lopez (2ndL) in the Men 800m Heat 1 event at the IAAF World Indoor Athletics Championships in Sopot, Poland on March 7, 2014 - by Janek Skarzynski
Dibaba has been in electrifying form this season, breaking three world indoor records as she looks to add the 3000m crown to the 1500m indoor title she won two years ago in Istanbul.
At the opening session in Sopot's Ergo Arena, the 23-year-old cruised through her heat, happy to sit near the back of the pack led alternately by Kenyan Irene Jelagat and Alia Saeed Mohammed of the United Arab Emirates.
Dibaba, sister of multi-world and Olympic medal winner Tirunesh, moved up the field effortlessly through the 2km mark and with three laps to go took the lead and upped the pace.
She finally clocked 8min 57.86sec, more than 40 seconds slower than the world record of 8:16.60 she set in Stockholm early last month.
"The race went very well," Dibaba said. "I didn't want to lead in the early laps, I only wanted to move up with five laps remaining and I executed my plan.
"I know I have a great time in this event and that gives me confidence... I don't think I'll have a hard time taking gold."
Dibaba will come up against Kenya's reigning indoor 3000m champion, Hellen Obiri, and Bahrain's Ethiopian-born two-time world 1500m champion Maryam Jamal in Sunday's final.
Dibaba's teammate Aman also advanced smoothly into the final of the men's 800m.
Aman bolted past Spain's Kevin Lopez at the bell and kicked home in 1:46.73 to win his heat and put him well on the way to defending the title he won in Istanbul as a junior.
"I'll do my best to take my second gold at my second championships," Aman said. "The race went great and I ran it as expected and the result was as I expected."
In-form South African Andre Olivier and Poland's two-time European indoor champion Adam Kszczot both looked comfortable winning the remaining two heats, with only the winners sure to qualify.
A second Pole, Marcin Lewandowski, also made the final, but world outdoor silver medallist Nick Symmonds of the United States missed out.
There was a huge scare earlier for Croatia's Vlasic, the former two-time outdoor and indoor world high jump champion missing the qualifying standard of 1.95m.
She eventually went through to the final with Belgium's Nafissatou Thiam in joint eighth place with a best of 1.92m and was eager to play down her morning session blip.
"My main and only aim was to qualify for the final," the 30-year-old said. "I don't know why, my leg fell asleep during the qualification.
"I only had two competitions before Sopot but I feel confident."
American Ashton Eaton took control of the heptathlon, on 2,012 points after a personal best 6.66sec in the 60m followed by a season's best of 7.78m in the long jump.
It left Eaton, the current world and Olympic decathlon champion, defending indoor heptathlon champion, and world record holder in both the decathlon and heptathlon, just 48 points shy of his equivalent total during his world record.
His Canadian wife Brianne Theisen Eaton was also well placed in the women's penathlon after two events, with the shot put, long jump and 800m to come in the gruelling one-day event.