A common topic in alternate history fiction works is the question what would have happened if a major war had been won by the other side. These usually focus on the events after the war, and the change itself is not depicted in a realistic way: it's either not discussed, or attributed to a superweapon or deus ex machina.
I know that WW2 was a very complex war, with a huge number of social and economic factors in it so that there was no single realistic "miracle" which would have guaranteed a certain different outcome, therefore I list a number of disclaimers, in order to make this question fit into the topic of this site.
It doesn't have to guarantee an Axis victory, but it has to significantly increase its probability.
A victory doesn't necessarily mean global domination (which neither power had any realistic chance of achieving). If Germany ends up in control over most of Eastern Europe (like the Soviets ended up doing in real life after the war), with a Soviet Union unwilling to fight, and with a peace treaty with the western Allies at least slightly favorable to Germany, it would count as a victory for Germany.
The change has to be a single event, or a collection of tightly coupled and interdependent events. It has to happen either during the war, or not more than a few years before it. The war should, at least in the beginning, look very similar to what happened in real life: the alliances should be roughly the same, the events like the conquest of Poland, the occupation of France, an attack against the Soviet Union, and a naval war between the USA and Japan should occur (or at least begin), even if at different dates or different order. The major participants should be the same.
The change should have a realistic justification (so no secret nazi superlaser), I would think in the following changes: events progressing slightly faster or slightly slower than in real life, a single large battle or series of interconnected battles won by the opposite side (if that had even a small chance of happening)
I'm thinking along the lines of Germany and its allies advancing faster against the Soviets and crushing them before they had any chance of putting up a good defense, or Hitler not antagonizing scientists so they could develop even better equipment or maybe even a nuclear bomb, or Japan winning the battle of Midway and keeping the USA from entering the European theater, or a different sequence of diplomatic events leading a peace on one front which in turn could lead to a victory on the other front, etc.