Japan has unexpectedly lost two key votes at a meeting of the International Whaling Commission (IWC) in the Caribbean island of St Kitts.
Whale meat consumption has gone down in Japan
The pro-whaling nation wanted to end work on conservation of sea mammals and introduce secret ballots.
Correspondents say for the moment at least the anti-whaling bloc appears to have retained the balance of power.
Japan says it will consider leaving the IWC if it does not move back towards a resumption of commercial whaling.
Japan has spent years lobbying developing nations to join the IWC and wrest power from the majority anti-whaling bloc. Environmental groups accuse these countries of voting with Japan in return for aid, a charge which the Japanese deny.
Conservation groups have expressed cautious relief.
The BBC's Richard Black in St Kitts says they believed a Japanese win on the conservation motion would have had serious consequences for many species of small cetaceans.
Not all of Japan's traditional allies have turned up here and a couple voted unexpectedly with the pro-conservation nations, he says.
However, other votes lie ahead during the five-day meeting and other countries expected to side with Japan may yet turn up, our correspondent says.
The basic argument is the same as it has been for years.
The self-styled pro-conservation countries led by Australia, New Zealand and the UK believe whales are intrinsically special animals and should never be killed.
In the opposition corner is a bloc led by Japan, which sees things differently.
Japan's deputy commissioner to the IWC, Joji Morishita, says the organisation has become too concerned with conservation.
Speaking on BBC Five Live Breakfast he said many Japanese people felt the IWC was "arrogant" and that whales could be used on a sustainable basis.
This meant "science and probably international law" were on the side of the Japanese, he said.
"Many of Japanese citizens think that Westerners, [the] outside world, are imposing their own value code on Japan on an emotional basis, and naturally they think they're bullies or... arrogant."
He added: "Allowing sustainable use of abundant species while protecting the depleted... we don't see the problem with that. It's exactly the same as conservation and management of any other wildlife or fishery resources."
But if the argument is familiar, the balance of power this year looks very different.
Four countries have just joined, of which three look set to support Japan giving it a majority on paper.
That could mean a number of important changes to the IWC.
Japan has hinted it may move towards overturning the 20-year moratorium on commercial whaling, although a vote for resumption of commercial hunting at this meeting itself is highly unlikely.
To try to erode Japan's support, environmental groups have been campaigning in some of the small developing nations which traditionally support Japan.
A survey commissioned by WWF suggested there was a majority opinion against whaling in all 10 of the Caribbean and Pacific states in which they polled.
WWF is urging delegates from those nations to cast their votes accordingly.