This was a tough match and the momentum switched back and forth from the moment the home side opened the scoring.
The result means a third successive Leeds-Saints Grand Final, while it is also the third year in a row that Wigan have bowed out at this stage.
Richards added the conversion for a two-point lead, a lead that was defended when Meli, like Richards, was ruled to have put his foot over the line in the act of touching down.
But Saints would re-take the lead before half time: with pressure mounting on the Wigan defence Sean Long found enough space to get over, Eastmond adding the conversion to make the score 10-6.
The hosts extended that advantage after the restart when Long’s well-aimed pass found Meli, who this time navigated perfectly the space between the corner post and the oncoming defenders.
The Warriors put themselves in a position to rescue the game when Tomkins’ pass set Richards loose, Richards then kicking to the in-goal area and re-gathering for an excellent try.
With the gap just four points Wigan did all they could to find a try that would level matters and with the kick at goal offer the chance of a narrow win, but St Helens held firm until full time.