As far as I know, there are several theories about the battle of Guadalcanal and its possible outcomes. One of them is that Japan could have won.
As we all know the battle took place in 1942, during World War II, when the US Marines landed on August 7th. It took Americans 6 months to defeat Japanese. The Guadalcanal is a part of the Solomon Islands which lie to the north-eastern approaches of Australia. The island itself is no use, except for the strategical means. It was important for both sides in Pacific war. For Japanese, it was a way to cut off the sea route between Australia and America. For Americans, it was the way to protect Australia from Japanese invasion. As we know, the battle ended with the Japan surrender, and it was the end of the World War II.
There is a version, that if Japanese would not start the Battle of Midway, they could fix their positions, wait for support and defeat Americans, for at that time Americans hadn't dug in yet and were low on supplies.
Another version states, that if Japan was able to knock out the few US carriers operational in the Pacific at the time, Guadalcanal could have been isolated and retaken. The few aircraft on that island could be beaten by a combination of naval bombardment and air strikes. US ground forces would not have lasted long without supplies and air cover.
Some other researchers state that there was a slight possibility to win. If only Japanese could know the number and locations of the few remaining Allied warships, and that the U.S. carriers had withdrawn from the battle area and would not be a threat the next day, they would be able to press on the attack on transport ships and the marines would be forced to withdrawn from the Guadalcanal. But that information was impossible to get at that time. So it happened the way we know it now.
Most of the theories agree that the win was possible at the very beginning of the Guadalcanal Campaign. Like, if Japanese had followed up their blitzkrieg on the US and Australian Navy at Savo Island, followed by a determined combined land, sea, and air effort to retake the island, they could have easily won the battle.
The topic is fascinating, so I would also encourage you to read more about it. Here are some investigations I’ve found useful: