Front-runner and Number one

Front-runner noun - A competitor thought likely to win.

Number one and front-runner are semantically related in leader topic. In some cases you can use "Number one" instead a noun phrase "Front-runner", when it comes to topics like precede.

Number one noun - The first or highest in an ordering or series.

Front-runner and number one are semantically related in precede topic. You can use "Front-runner" instead a noun phrase "Number one".