ANYONE involved in the event would never admit it, but the US PGA Championship is undoubtedly seen as the least important of golf's four majors.

The Masters has the benefit of being the first of the season and also being staged every year at Augusta National, an iconic venue that every serious fan knows well.

The US Open has the reputation as the toughest test, while the Open Championship is the most historic, as well as taking place on some of the best links courses in Britain and Ireland.

Grammatically dubious slogans such as "Glory's Last Shot" and the current "This is Major" have failed to change the image of the US PGA, but the tournament can rightly claim to have produced the most thrilling major of 2014.

The back nine at Augusta last year failed to produce any of the traditional fireworks as Bubba Watson ground his way to a second green jacket, while Martin Kaymer and Rory McIlroy were always in command of the US Open and Open respectively.

In contrast, the result at Valhalla – and indeed whether the tournament would be held over into Monday – was in doubt right until the final hole, when McIlroy completed a closing 68 to finish 16 under par, one shot ahead of Phil Mickelson after a remarkable final day which finished in near-darkness, with the lights blazing from the clubhouse behind the 18th green.

Twelve months on, McIlroy has somewhat surprisingly recovered in time from a serious ankle injury – suffered while playing football on July 4 – to defend his title and has been paired with the year's major champions, Jordan Spieth and Zach Johnson, for the opening two rounds.

Talk of a rivalry between McIlroy and Spieth, which appeared premature when the latter won the Masters, was given legitimacy when Spieth also claimed the US Open and came agonisingly close to keeping the grand slam dream alive in the Open at St Andrews.

And although golf's many variables mean that the pair may rarely do battle in the closing stages of majors, it will be fascinating to see how they fare on Thursday and Friday at Whistling Straits.

The last time they were paired in a major was in the 2014 Open, when McIlroy shot 66, 66 on his way to victory and Spieth could only manage scores of 71 and 75 before finishing tied 36th.

One Man who will be taking the tournament seriously, mean while, is England's David Howell, after qualifying for his first US PGA Championship for eight years.

In 2006 Howell was inside the world's top 10 after outscoring playing partner Tiger Woods to win the HSBC Champions in China before winning the BMW PGA Championship and helping Europe to a record-equalling Ryder Cup victory in Ireland.

By October 2010, a number of injuries and a loss of form meant Howell was ranked 569th in the world and it took until his victory in the Dunhill Links at St Andrews in 2013 for him to celebrate reaching the end of what he called a ''long, long road from the depths of despair".

The 40-year-old was unable to claim a sixth European Tour title in 2014 and was ranked 150th earlier this season, but finishing third in the Saltire Energy Paul Lawrie Matchplay at the start of August lifted him from 104th to 86th in time to secure his place at Whistling Straits.

"Right from the word go this year I thought to get into the top 100 from where I was I would need to play some nice golf and make some nice progress, and I've just about done it," Howell said.

"That's where I want to be. We all want to be in the top 50 and I'm some way off that, but heading in the right direction by playing the majors and being around those (top) guys again.

"I wouldn't say it's half the battle, but it certainly makes it easier and you feel a bit better about yourself when you come back and play in the non-majors as well."

Howell made his US PGA debut at Whistling Straits in 2004 and was two under par after the third round before a closing 75 saw him slip to share of 45th.

"I played it in 2004 so I know the course somewhat," added Howell, whose best finish in a major is a share of seventh in the Open Championship at Royal Birkdale in 2008.

"It's a big old test but I am looking forward to it. It's an impressive golf course, quite intimidating visually but I did all right there in 2004. I had a bad last round to finish 45th but was in reasonable shape with a round to go so it shows I can play it.

"After eight years it's good to be back in the US PGA. I managed to get in the Open and I didn't try and qualify for the US Open. I felt that was a mistake and I regretted it."