The 27-year-old Annu sent the iron spear to a distance of 62.43m in her second round throw, bettering her earlier national record of 62.34m, which she achieved in March, to book a place for Tuesday’s final.
In the process, she became the first Indian to reach the final of the women’s javelin throw in the World Championships.
Annu finished third in Group A and qualified for the final as the fifth best performer of the qualification round.
Only two javelin throwers, Asian champion Lyu Huihui (67.27m) of China and Christin Hussong (65.29m) of Germany, could cross the automatic qualification mark of 63.50m while another 10, including Annu, made up the 12, who will compete in the final.
Annu opened with a 57.05m before coming up with her career-best throw in the second round. She had a 60.50m in her third and final throw.
World leader and Asian Games champion Liu Shiying (63.48m) of China and Ratej Martina (62.87m) of Slovenia finished ahead of Annu in Group A, while reigning Olympic champion Sara Kolak of Croatia was sixth with a best throw of 60.99m.
The other two Indians who competed on Monday, Archana Suseentran and Anjali Devi, failed to go past the first round in the women’s 200m and 400m, respectively.
The 25-year-old Archana, who got a last minute invite from the world governing body IAAF to take part in the showpiece, finished last in heat number 2 and 40th overall out of the 43 participants who completed their races, with a time of 23.65 seconds. She has a personal best of 23.18.
Dina Asher-Smith of Great Britain, who had won a silver in the 100m dash on Sunday, topped the overall timings chart of 200m first round heats with 22.32 seconds.
The 21-year-old Anajli, meanwhile, finished sixth in heat number 6 and 37th overall out of 47 athletes, with a time of 52.33 seconds.
Anjali, who underwent a confirmatory trial before being cleared for this championships, has a personal best of 51.53, which she achieving while winning gold during the Inter-State Championships in August in Lucknow.
The top three finishers in each of the six heats and the next six fastest qualify for the semifinals. The slowest time that made the cut for the semifinals was 52.23.