Stockholm: Two-time champion James Blake displayed best form of the season so far, while he beats  second seed Juan Martin del Potro in a two setter, 6-4, 6-4 on Wednesday to reach the quarterfinals of the Stockholm Open.

The win gave the 69th-ranked American, the champion in 2005 and 2006, his first quarter-final since making the last eight in the Swedish capital a year ago.

After facing a season full of injuries, the 31-year-old Blake has spent several weeks this season playing Challenger events, winning two of the lower-level titles and the American said he's not felt this good in years.

"This is my best win of last three years," said Blake and added, “This is the best I've felt on court for a long time.”

"I've not done this for four or five years. I'll be proud of this one for a long time. The way I played today was what it felt like when I won here. Back then things came a little easier and the body recovered quicker. But I'll take it easy tomorrow, I think my game and my experience has helped me." said Blake

Del Potro was competing this week for the first time in a month as he eyes the Davis Cup final against Spain in December.

"He played better than me today -- it's over for this week. I have a few days now to be ready for next event. I must work very hard." said Del Potro

Blake won the first set in 49 minutes with a stinging reflex return at Del Potro's feet on set point and secured victory with a break in the final game of the second set with a volley winner into the open court.

The American improved to 17-2 in Stockholm and is likely to face Argentine David Nalbandian in the quarter-finals if the South American beats Croatian Ivan Dodig.

South African fifth seed Kevin Anderson moved into the next round with a 6-7 (3/7), 6-4, 6-4 comeback win over German Tommy Haas.

Anderson broke once in each of the last two sets and fired 21 aces and 55 winners to move into a match against either top seed Gael Monfils or Australian Bernard Tomic.

"I'm really, really happy to get through. My serve was the biggest positive today.I served much better than my first match. It was tough to break Tommy but I managed one in each set." said Anderson.

Tomic tamed Estonian qualifier Jurgen Zopp 7-6 (7/5), 4-6, 6-0 to set-up a date with Monfils, who had a first-round bye and is making his Stockholm debut.

Monfils, still theoretically in the chase for a spot in next month's eight-man World Tour Finals in London, will be testing a knee injury which forced him to miss last week's Shanghai Masters, where Tomic earned a top 10 win over American Mardy Fish.

Canadian sixth seed Milos Raonic continued his successful Stockholm debut by reaching the quarters with a 6-3, 6-3 over German Philipp Petzschner.

Bulgarian prospect Grigor Dimitrov, coached by Australian Peter McNamara, advanced as he put out American Ryan Sweeting 6-3, 6-1 with six aces and four breaks of serve.