"The TDP will be a part of the NDA now... Chandrababu Naidu will be the co-architect with Narendra Modi in creating a corruption and Congress-free India," said Naresh Gujral of the Akali Dal, another partner of the BJP in the National Democratic Alliance or NDA.
The partnership with Mr Naidu, 63, could propel the Modi-led BJP closer to the 272 seats it needs to form the next national government. Mr Naidu hopes the partnership will give him another shot at being Chief Minister, this time of the down-sized Andhra Pradesh, once the new state of Telangana is carved out of it on June 2. (Elections: full coverage)
"We have taken this decision for the people of this state...The BJP will contest five Lok Sabha seats and 15 Assembly seats in Andhra; in Telangana it will contest eight Lok Sabha seats and 47 Assembly seats," Mr Naidu announced.
Local BJP leaders in Telangana have threatened to resign. Mr Naidu, who was cagey about whether he supports the bifurcation of Andhra Pradesh, is expected to be spurned by Telangana voters for not championing their cause. For the same reason, he is likely to be rewarded in the regions of Seemandhra that will form the residuary state.
These areas have aggressively opposed the new map, not least because they will grapple with a reduced share of water and revenue from Telangana.
Some TDP leaders have opposed the alliance too; they do not want to give away seats like Vijayawada central and Malkajgiri to the BJP.
NDTV's opinion poll shows a big leap for Mr Naidu in Seemandhra; his party gets 14 of the 25 parliamentary seats, according to the forecast. That's a gain of 10 from 2009. (NDTV Opinion Poll: Chandrababu Naidu makes big gains in Seemandhra)
Of the 17 seats in Telangana, the Congress and K Chandrasekhar Rao of the TRS will get seven each, the poll forecasts. The TDP lands two.