Teenager Ghirmay Ghebreslassie won Eritrea's first gold medal at a World Championships, while 800m champion Mohammed Aman started well.
Ghirmay Ghebreslassie made history for Eritrea in the marathon, while defending champions Abeba Aregawi and Mohammed Aman made solid starts at the World Championships in Beijing.
Ghebreslassie became the youngest winner of the men's marathon, the 19-year-old also winning the north-west African nation's first gold medal at the IAAF showpiece when he stopped the clock at two hours, 12 minutes and 28 seconds.
Ethiopia's Yemane Tsegay (2:13:07) finished second in a season-best time, while Ugandan runner Solomon Mutai (2:13:29) won bronze.
Women's 1500m champion Aregawi was third in her heat on Saturday, clocking 4:10.77 to progress to the semi-finals with few concerns.
Ethiopia's Genzebe Dibaba (4:02.59) went fastest in the three 1500m heats - the time quicker than Swede Aregawi's winning time in Moscow (4:02.67) from two years ago.
Dibaba's countryman Aman won his men's 800m heat in 1:47.87, guaranteeing the 21-year-old a spot in the semi-finals.
Kenya's Ferguson Cheruiyot Rotich (1:45.83) went quickest in the six heats, while countryman David Rudisha - the Olympic champion - won the final heat in 1:48.31.
In the field, Poland's Pawel Fajdek set the benchmark in the men's hammer throw qualifying with an effort of 78.38 metres - while German Christina Schwanitz was one of three competitors in the women's shot put to usurp 19m, registering a 19.39m effort.
Nadine Visser set the early pace in the women's heptathlon, running 12.81secs in the 100m hurdles, but Olympic champion Jessica Ennis-Hill is 30 points clear after two events - the Briton registering a mark of 1.86m in the high jump.
Barakat Al-Harthi of Oman, ran a 10.31secs in the preliminary men's 100m - getting himself into the heats.
Al-Harthi, Fiji's Banuve Tabakaucoro (10.50secs) and Suriname's Jeffrey Vanan (10.55secs) were the preliminary heat winners.