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The South African-born left-armer claimed five for 54 to help dismiss Auckland for 221 on the opening day of a Plunket Shield match at the University Oval yesterday.
At stumps, Otago was 118 for two and in a good position to build a big first innings lead.
Wagner took a memorable hat trick in Queenstown two summers ago, when he became the first person in the history of first-class cricket to take five wickets in a six-ball over.
He also achieved a hat trick in South Africa before moving to New Zealand. Now he is on the cusp of a third hat trick, having claimed the last two wickets of the Auckland innings from consecutive deliveries .
He nicked out Michael Bates and bowled Bhupinder Singh to complete his 12th first-class five-wicket bag.
Earlier, he made the initial breakthrough with a fine delivery which nipped away from the right-handed Michael Guptill-Bunce and took the edge. He also snuffed out the dangerous Craig Cachopa's innings before he could get established, and claimed Gareth Hopkins' wicket just before lunch, when the captain tried to glance a delivery but only got a faint connection which carried through to the keeper.
''It is just nice to be in the wickets column after a bit of a dry season, I suppose,'' Wagner said.
As for the impending hat trick: ''It is not something you think about too much,'' he said.
''I just have to focus on bowling the ball in the right place but if I end up getting a hat trick it would be nice.''
''But we've got to do a lot of batting [today]. Losing those two wickets at the end of the day is something we would have liked to have done differently.
''And I think we let it slip with the ball. We bowled well in patches but there was enough there to restrict them to a lower total.''
Auckland made the confident decision to bat first, despite the presence of the some helpful cloud cover for the Otago bowling attack.
James McMillan settled into a great length and got the ball to swing, and swing late.
Initially, Auckland combated the movement quite well with inexperienced pair Guptill-Bunce and Michael Barry valuing their wickets.
Wagner removed Guptill-Bunce and McMillan struck in the next over with gem of a delivery which the left-handed Barry guided into the slips.
Zimbabwean-born all-rounder Colin de Grandhomme did not do his side any favours when he wafted at a wide delivery and gave the slip cordon more practice, and just before lunch Hopkins perished, leaving his side 66 for five at the break.
Dusan Hakaraia (23) and Anaru Kitchen (74) helped bring some scoreboard respectability, combining to put on 83 for the seventh wicket.
Hakaraia, though, made the sinful decision to play the off-spinner Mark Craig against the spin and was rightly bowled.
Sam Wells removed Kitchen, who played around a straight delivery after having batted quite nicely. He whacked three sixes and eight fours in a commanding innings.
Bruce Martin provided some useful resistance with 31 before he was also bowled by Wells.
Aaron Redmond made a rollicking start for Otago, whacking two sixes over third man off the rapid bowling of Lachie Ferguson. The 21-year-old generated some real pace but he was wild with it and Redmond used the bowler's speed to ramp the ball.
He followed up with a thunderous cut shot through point and a spanking drive. After three overs Ferguson had gone for 22 runs and Redmond was well on the way to his 36th first-class half century.
On 72, he ramped another delivery from Ferguson in the direction of the rope at thirdman but de Grandhomme intercepted the ball with a marvellous one-handed catch. With an eye seemingly always on the rope, he leaped high and plucked the ball out of the air with his right mitt and then did well to land back in the field of play.
Redmond and Broom had combined for 111. But some of the good work was undone when Broom was enticed into a drive and nicked out for 35 in the penultimate over of the day.