New Delhi: Indian boxers packed a powerful punch as Commonwealth Games medallists Manoj Kumar (64kg) and Jai Bhagwan (60kg), along with rookie teen sensation L Devendro Singh, qualified for the London Olympics by advancing to the World Championships' quarterfinals with contrasting wins in Baku, Azerbaijan on Tuesday.

While Manoj rallied to defeat China's Qing Hu 17-15, 19-year-old Devendro continued his giant-killing spree by beating seventh seed Carlos Quipo of Ecuador 18-12 in another impressive performance. In the evening session, Jai upstaged seventh seed David Joyce of Ireland 32-30 in a tense battle.

The trio sealed their berths for the Olympic Games, becoming the first lot of Indian boxers to qualify for the mega-event.

Top 10 boxers (from 49kg to 81kg) at this event will make the Olympic cut while boxers in the 91kg and +91kg category will have to finish among the top-six to book their London tickets.

But, there was some disappointment too for India as Asian Games silver-medallist and 12th seed Dinesh Kumar bowed out with a 7-16 loss to CWG gold-medallist Damien Hooper of Australia.

Manoj was the first to take the ring for India and the counter-puncher, who has won the coaches' admiration for his calculative approach and adaptability, once again impressed with a composed performance.

The Haryana-boxer was trailing 3-6 in the opening round but he bounced back brilliantly to level the score 7-7 in the second round and narrow the overall gap to 10-11.

He went on the offensive in the final round, securing seven points against his rival's two to clinch victory. Manoj will now face fifth seed Thomas Stalker of England. Stalker, a European Championship silver-medallist, defeated Russia's Alexander Solyanikov 17-9.

"My focus was on tiring him down and this is the reason why I was down by three points in the opening round because I kept my guard and was focusing on defence. But this tactic ultimately paid off as he was tired and I managed to go on the offensive," said Manoj.

Next up was the spunky Devendro, competing in his maiden senior international event, and he once again displayed nerves of steel against his more fancied rival.

The nimble-footed teen from Manipur took a 5-2 lead in the opening round, capitalising on his opponent's overtly defensive approach with some telling body blows.

"I was under immense pressure before this bout. It was once in a lifetime opportunity I did not want to miss and I think it helped me in the end to strain myself a bit before the bout," Devendro said from Baku.

Although his rival became more aggressive in the next two rounds but Devendro managed to negate that with his precise straight body blows and hooks to seal the issue comfortably.

"I had fought with him during our recent training trip to France where he was among those I sparred with. That gave me a good idea of his game and it helped me in this bout," he said.

Devendro will next face Korea's Shin Jong Hoon, who defeated France's Jeremy Beccu 22-10.

But Dinesh's loss came as a dampener in the day session of the mega-event as he paid the price for relying too much on power then movement against an agile rival, who impressed with his ring craft and reflexes.

In the evening session, Jai opened the his bout confidently against a higher-ranked opponent and led 13-8 in the first round. But he lost focus in the second round as his rival roared back to notch up 10 points against Jai's seven to make it 18-20.

The third round turned out to be dramatic as both Jai and Joyce were warned twice by the referee. While Jai was penalised for clinching his rival too much, Joyce was docked four points for using his fist to hit Jai at the back of his head. The round ended 12-12 but the Indian came out trumps overall.

"He was of short height and it is difficult to control a guy like him because such boxers are very quick on their feet but after I managed secure a good lead in the opening round, I could win. As for warnings, it happens, I am just glad it didn't affect the result," he said.