JAMES WARD is Britain's secret agent in the Davis Cup.

Yesterday he went one step further by pulling off mission improbable, if not impossible, against Big Bad John. Typically for an Arsenal fan, there was much to admire about the way he went about things against John Isner, the 6ft 10in World No 20 from Greensboro, North Carolina, but unusually there was also the tangible end product of a gutsy triumph against a powerful world class opponent.

You would have thought his cover would have been blown by now. Before today Ward already had nine Davis Cup singles victories on his resume, one more than the American could boast from the same amount of matches. His previous best was a five-set dismissal of Sam Querrey of the United States at precisely this stage of proceedings during the previous meeting between these two founding Davis Cup teams on the clay of Petco Park, San Diego in January. But even that couldn't hold a candle to this one.

As afternoon turned into early evening, this son of a London cabbie utterly enthralled a capacity Glaswegian crowd by patiently navigating his way past the 20th best tennis player in the world from two sets to love down. Five match points had come and gone, and four Ward toilet breaks had been taken, by the time one last backhand volley into the net saw Isner cut down to size by a 6-7 (4), 5-7, 6-3, 7-6 (3), 15-13 scoreline. The 29-year-old American, you may recall, famously triumphed in the longest tennis match in history - the match with Nicolas Mahut at Wimbledon 2010 which took 11 hours and three days to complete - but by the end even the marathon man had been outrun.

The 28-year-old Londoner encountered significantly less difficulty winning over the affections of the Emirates Arena audience. Bounding out on court to the strains of 'Start me up' by the Rolling Stones, and acclaimed by the Friday afternoon beer drinking crowd as Jamesy, the sobriquet usually reserved for Rab C Nesbitt's pal, he shouldered the task of following the Andy Murray with aplomb, clad in a fetching Paisley pattern Ted Baker t-shirt. USA captain Jim Courier had spoken on Thursday about the 'political undercurrent' to this match, but the post-referendum Glasgow crowd embraced him as their own and if there was one Ward rode that wave to success.

There was no disguising the scale of this task. Despite a morale boosting win against his opponent during a pre-Australian Open exhibition event at Kooyong this January, Ward had 91 spots in the world rankings to scale. These two occasional practice partners know each other's games well.

In Isner's case, that means watching a punishing array of serves, sent down at velocities of anything up to 140mph and heights, when you include outstretched arm and racket, approaching 9ft, whistle past you. While the 27-year-old had suggested that the slow indoor courts chosen by the host side were partially to slow him down, there was little evidence of that. A small posse of American fans held up numbers denoting his ace count, and by the end they were holding up a '3' and '9'. Either that or they had lost count. Fully two hours of play had elapsed before Ward was able to subject him to a single break point.

At least, though, from the outset the Londoner was winning his own service games. We were into the fourth game of the match by the time any points on service were surrendered. Few coupons were burst by the fact that the first set arrived at a tie-breaker. Isner sets usually do.

But Ward was feeling pretty good about himself, gesturing to a Glasgow crowd which needed little encouragement. The net, however, wasn't quite so helpful. Ward was a mini-break to the good at 4-2, when a flat Isner ground stroke pummelled it before somehow climbing over. The wind removed from his sails, and firmly at Isner's back, he surrendered the set without winning a further point.

The second set merely provided second helpings of the same fare. But just when Ward appeared to be hanging on to take us to a second breaker, our first break of serve arrived in the 11th game of the set. Isner served out comfortably, Ward left half volleying the ball away, like a disconsolate Arsenal centre half, into the crowd.

At that point it seemed like Taxi for Ward. But as formidable an advantage as that giant frame gives Isner, it isn't exactly the optimal build for a tennis player. Lugging it around for the rigours of a five-set match isn't ideal, but it still took some inspired play from Ward to give himself a toe-hold in this match. Having executed an exquisite running pass to circumnavigate the giant American at the net to set up his first break point, he then repeated the feat to go 4-2 up in the third, his momentum carrying him joyfully around the net in celebration.

If you squinted your eyes a little bit, you could almost have sworn it was the World No 5, but then the main factor credited with Ward's giant strides has been an invite to those punishing training blocks with Murray in Miami. As he served out for the set, one errant Isner swipe saw a ball strike the Emirates Arena ceiling, while the roof was nearly raised when the set was put on the board, courtesy, somewhat ironically, of a Ward ace.

The match had been re-calibrated at a new equilibrium now, Ward dealing more comfortably with his own service games, yet seeing a break point opportunity come and go. When Isner mistimed a simple lob, it suggested the big man was getting lethargic.

Ward pumped up the crowd again going into the fourth set breaker, and rode a wave of momentum and Isner mistakes when he got there. A sweet backhand pass gave him an early advantage, even the net returned the favour for its earlier spite, and before long he was going for his third toilet break of the proceedings to compose himself for a fifth set.

From the moment during the second set when he arrived courtside, no-one led the cheers, cajoling and advice more fervently than Andy Murray. Those beach runs came in handy during a stamina-sapping, taut, 111-minute final set, which saw Isner somehow saved five match points, with Ward digging deep to save two break points. Some of Ward's moments were Murray-esque in their execution; others not so much. But by the end the biggest surprise of all at the Davis Cup yesterday was the fact that an Englishman may even have outshone a Scotsman. He may also have earned him a day off.