Rudisha, whose world record stands at one minute 41.01 seconds, is the overwhelming favourite to take the 800 title in London after missing out on selection for Beijing four years ago through injury.
"The track is fast. It looks good," the 23-year-old world champion told reporters through a translator.
"In this championship I don't look at the record. It is a medal that I want. Once I get the medal, toward the end of the season I can think about the record."
Algerian Taoufik Makhloufi's brief appearance in the 800 heats appears to have dashed his medal hopes in the 1,500 after he was disqualified from all further events in the athletics competition because the referee considered that he had not provided a bona fide effort.
Makhloufi, who beat champion Asbel Kiprop in Tuesday's semi-final of the 1,500, jogged for 200 metres before stepping off the track. He had been confirmed in the two-lap race by his team the previous day and so had to run, the IAAF said.
It was a different story for Australia's gold medal favourite Sally Pearson, who went all out in the 100 hurdles to record the fastest first-round time at an Olympics with 12.57 seconds.
But there were tears for women's 1,500m medal hopeful Genzebe Dibaba, younger sister of Ethiopia's 10,000 champion Tirunesh, who was taken off the track in a wheelchair clutching her hamstring after struggling in her heat.
Belarussian Nadezhda Ostapchuk topped qualifying for the women's shot put final later on Monday (19:15 local time) with 20.76 metres just ahead of her arch rival, world and Olympic champion Valerie Adams of New Zealand (20.40).
There was also plenty of home success in the morning qualifiers to keep the cheers rolling around the stadium. Lawrence Okoye sealed a place in Tuesday's men's discus final with a throw of 65.28.
"The whole team is feeling pretty positive at the moment, the story's going round about how the crowd is unbelievable and I witnessed it myself today," said Britain's 800 metres runner Andrew Osagie, who finished third behind Rudisha to make the next round.
Rudisha took the lead in his heat as the athletes broke from their lanes and gently increased his long, loping stride over the final lap for a straightforward victory in one minute 45.90 seconds.
The only man to have beaten Rudisha over 800 since 2009, Ethiopia's Mohamed Aman, also made Tuesday's semi-finals, winning a pedestrian race in 1:47.34.
Kenya's Wilfred Bungei won the title in 2008 but retired two years ago.
Pearson overcame her nerves to dominate her hurdles heat, finishing almost 0.5 seconds clear of runner-up Reina-Flor Okori of France.
"I was nervous about the first race," the world indoors and outdoors champion said.
"It is the Olympic Games. If I don't feel nervous, I'm not ready so I am glad I had nerves today."
She will line up against Lolo Jones in Tuesday's semis after the American, who fell in the final in Beijing when leading the race, won her heat in a season's best of 12.68.
Jones offered her sympathy to former world champion Brigitte Hylton-Foster, who missed out on qualifying after hitting the fifth hurdle in her heat.
The 37-year-old slapped the track in frustration after she crossed the line in seventh.
"My heart just breaks for Brigitte," Jones said. "Honestly, the emotions were out for her. If she had punched me I would have understood."
Kellie Wells, the only woman to beat Pearson this year, and defending champion Dawn Harper both made it through to the next round.
The highlights of the evening session are the men's 400 and 400 hurdles finals, the women's 3,000 steeplechase and the women's pole vault final, where Russian Yelena Isinbayeva will be out to win a third straight gold medal.
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