Tries: Ah Van 2, Hanbury, White 2, Haggerty, Cahill
Goals: Ah Van 5
St Helens (28) 40
Tries: Jones 2, Wellens 2, Flannery, Hohaia, McCarthy-Scarsbrook
Goals: Lomax 6
St Helens survived a late fightback by spirited Widnes to book a place in the fifth round of the Challenge Cup.
Patrick Ah Van's early try and Rhys Hanbury's solo score gave Widnes hope.
But Saints looked out of sight when they led 40-16 after 54 minutes when Paul Wellens scored his second and his side's seventh try.
Yet, with James Roby sin-binned, Widnes hit back and scored late tries through Hep Cahill, Ah Van and Lloyd White to just come up short.
Hanbury scores scintillating try
Saints, who last won the competition in 2008, were hot favourites against a Vikings side sitting bottom of Super League with two wins from their 11 games, and especially given the rich vein of form they had shown in winning three of their four fixtures since the departure of coach Royce Simmons.
But it was the Vikings who got off to the best possible start when Ah Van outpaced Wellens to score in the corner.
The lead did not last long as 18-year-old Josh Jones crossed wide on the left for his first Saints try, before Wellens touched down next to the posts to give them the lead after Jonny Lomax punched a hole in the home defence.
Lomax added the extras but Widnes were soon level at 10-10 when Hanbury brilliantly jinked his way past three defenders to score under the sticks and hand Ah Van the simplest of conversions.
But St Helens upped the tempo and eased clear with three more tries before half-time.
Saints disappointed despite win
Lomax's well-timed pass sent Chris Flannery over before Lance Hohaia touched down on the stretch and Louis McCarthy-Scarsbrook capitalised on more pressure on the Widnes line to cross and give Saints further breathing space.
White dummied his way over at the start of the second half to narrow the gap and give Widnes hope, but that was soon extinguished when Jones crossed for his second try to cap a fine passing move.
Wellens also scored his second when he burst on to Lomax's perfectly weighted grubber kick to seemingly put Saints out of sight, but still the Vikings would not give in and grabbed their fourth try when Kurt Haggerty powerfully forced his way over.
Saints finished the game with 12 men when Roby was sent to the sin-bin for attempting to punch the ball out of Jack Owens' hands after it had gone over the dead-ball line.
Widnes soon capitalised on their numerical advantage when Cahill twisted his way over.
But there was to be more late drama when the video referee ruled Ah Van had stayed in play when he dived over in the corner, and White crossed for a second time.
That left Widnes with only seconds remaining to try and complete a remarkable turnaround, and although they tried to pass their way up field the ball went dead and referee James Child's whistle ended their hopes.
Owens, Flynn, Dean, Isa, Ah Van, Craven, Hanbury, Cross, Clarke, Pickersgill, Winterstein, Haggerty, Cahill.
White, J. Kite, Leuluai, Mullally.
Wellens, Swift, Shenton, J. Jones, Meli, Hohaia, Lomax, Perry, Roby, Laffranchi, Flannery, Soliola, Flanagan.
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