The group - looking sophisticated in dark trench coats - opened with rock number When You're Looking Like That from their 2000 album Coast to Coast. There was a definite effort to show they had grown up since their start nearly 14 years ago, but their clear, strong vocals still had a youthful charm.
The boy band cracked jokes, filmed the crowd, encouraged fist-pumping and singalongs - and won the audience over utterly, even singing Happy Birthday to one lucky girl.
The obvious camaraderie between the four just added to the charm - seeing Westlife live brought home just how well they share the singing and the spotlight.
The band performed old hits such as Flying Without Wings and My Love, and showed off their harmonising in a powerful rendition of the Irish classic You Raise Me Up.
They also proved themselves to be kings of covers, delivering Coldplay's Viva la Vida, Rihanna's Only Girl (In the World) and Lady Gaga's Bad Romance. They even did a version of (I've Had) the Time of My Life, from the 1987 film Dirty Dancing and recently sampled by the Black Eyed Peas.
In the end, it wasn't Westlife who was lacking, but the venue and the crowd. The speakers crackled on louder and higher-pitched songs, and the lighting effects were limited in range. And even though the front rows were filled with diehard fans, behind them, the audience's enthusiasm eventually faded.
Perhaps the varied audience is a result of Westlife's broad appeal; plenty of older couples were among younger fans.
The whole affair was a nostalgic throwback to the late 1990s. From wearing Mickey Mouse graphic tees to dancing synchronised moves across the stage, Westlife proved they are still boys at heart.
And the crowd - rising to their feet in the encore, a rendition of the old-school number Uptown Girl - proved that some things never get old.