After Roger Federer kicked off Group B with a comfortable victory over Janko Tipsarevic, it was left to two counterpunchers of contrasting styles to give the crowd its money’s worth.
They did not disappoint, with fourth-seeded Spaniard Ferrer – hot on the heels of his Paris Masters victory – clinical in taking the first set by defending a solitary break with comfort, while sixth-seeded Argentine Del Potro showed great fight to force a decider.
Ferrer’s class looked like it might tell when, early in the third set, he broke Del Potro to 15 with a lovely bending forehand. The 6’5” Argentine battled back brilliantly though, breaking back at 2-4 down as he unleashed a succession of booming winners from the baseline.
But Ferrer would not be denied, breaking back to love at 5-4 to claim the victory in two hours and 16 minutes as Del Potro went long under sustained pressure from deep.
Next up for Ferrer is Federer, who the Spaniard has never beaten.
“I am very happy, it was a very beautiful, very tough and difficult match to beat Juan Martin,” a jovial Ferrer said afterwards. “But I hope that people here go home enjoying our tennis.
“It’s very bad news (to be facing Federer)! I don’t know what the secret is, maybe you can help?”
Ferrer may have come off the back of his first Masters 1000 crown, but Del Potro – resurgent after two injury-ravaged years – is in decent form himself after winning in Basel.
The Argentine powerhouse was a touch off the pace in the first set, repeatedly underhitting forehands to net and throwing in a few double faults for good measure.
But he matched Ferrer in the second and took his chance when it was presented, although Ferrer’s pair of missed forehand drives were only inches wide as he spurned game point to be broken at 1-2.
By now both men were serving crisply, with Ferrer dogged from the baseline and Del Potro unleashing powerful winners to turn the crowd on his side.
Del Potro’s game is high-risk though, and one of his brutal attempted winners landed long to put him 0-30 early in the decider. Ferrer pounced, with some lovely angled forehands, and he seemed in full control.
Neither man knows how to give up though, and Del Potro’s booming forehands found their range at 2-4, sending Ferrer off balance on three occasions as he cancelled out the Spaniard’s advantage.
Ferrer is a wily old fox though, and when his running drive across court gave him the first point at 5-4, he sniffed a chance to finally close it out – which he did through a combination of some overhit Del Potro forehands, and a rasping return that the Argentine could only spoon into the net.
The action continues on Wednesday, with Andy Murray and Novak Djokovic resuming their rivalry in South East London.
Tuesday's results from the ATP World Tour finals:
4-David Ferrer (Spain) v 6-Juan Martin Del Potro (Argentina) 6-3 3-6 6-4
2-Roger Federer (Switzerland) beat 8-Janko Tipsarevic (Serbia) 6-3 6-1