Drive to be the best prevents Serena from being too serene

Despite everything that Serena Williams has won and done, her sense of self can still fluctuate based on the outcome of a particular match.

It doesn't always seem to matter that she owns a record-tying 22 major singles titles heading into the US Open, which begins on Monday under a retractable roof on Arthur Ashe Stadium for the first time.

It's not necessarily a big deal to Williams that she's spent the past 3 1/2 years entrenched at No 1 and is the oldest woman ever to top the WTA rankings.