Serena getting closer

Serena Williams survives second-round test against world No 110 Kiki Bertens to continue bid for calendar Grand Slam at US Open

• Serena Williams found it tough going in her 7-6, 6-3 victory against Kiki Bertens at Flushing Meadows

• The world No 1 trailed 2-4 in the first set and 0-4 in the tiebreak before going on to claim the win

• Williams is bidding to complete the calendar Grand Slam in New York for the first time in her career

By Mike Dickson for the Daily Mail

Many of her challengers have already fallen, but Serena Williams's tortured demeanour showed that she is no certainty to complete the calendar year Grand Slam.

The world No 1 was agonisingly tight as she squeezed through to the US Open second round, 7-6, 6-3 against the unfancied Kiki Bertens of Holland, fortunate not to have gone to three sets.

Williams, who has seen the top seeds in her half scatter, trailed 2-4 in the first set and 0-4 in the tiebreak before nerves got the better of her unheralded opponent. It left the impression that the favourite could yet beat herself between now and a week on Saturday.

 Serena Williams celebrates as she beats Kiki Bertens in a tough second-round test on Arthur Ashe Stadium on Wednesday

 Williams lets out a roar as she ensures that the possibility of a calendar Grand Slam is still on at the US Open in New York

 Williams hits a backhand off one leg during her second-round clash with qualifier Bertens, of Holland

 Williams' frustrations were clear to see throughout the straight-sets victory on Arthur Ashe Stadium

At times there were shades of the French Open, where she loudly berated herself and kept falling behind before battling to the title that kept her on the road to becoming the fourth woman to win all four Majors in the same season.

Bertens, a qualifier ranked 110 in the world, benefited from ten double faults and 34 unforced errors donated by the American, but as ever Williams was able to find a way to win in the end.

'I took it one point at a time in the tie-break and next thing I knew it was 4-4,' said the defending champion.

'It doesn't worry me, being down a lot, I know I can try to make a comeback.

'I never stop, I keep going and give it the best effort I can.

'I've been really relaxed usually, today I was a little tight.

'It showed a bit but hopefully I can get back to where I was before.'

 Williams can't hide her annoyance at her performance against Bertens during the Wednesday day session

 Williams gestures towards her box in the stands (above), before letting out a scream of celebration as she fights off Bertens' challenge

 Williams has a look of determination on her face as she charges forward from the baseline to chase down a short ball

 Williams fires down a serve on Arthur Ashe Stadium before going on to close out the match in straight sets

Should Williams win her fourth consecutive US Open,she would become the fourth woman to sweep all four grand slam singles title in one season following Maureen Connolly (1953), Margaret Court (1970) and Steffi Graf (1988).

Williams next faces Bethanie Mattek-Sands, who beat fellow American CoCo Vandeweghe in straight sets in her second-round match.

'Bethanie's really good, she has a very aggressive game,' Williams said.

'I wasn't surprised with her win today, she's a great person, I love her, it will be a really difficult match.

'It will be very tricky and I'll have to play better if I want to win.'

 Williams stretches out to her right to play the backhand return from the Bertens serve on Wednesday afternoon

Williams seemed more relieved than anything else. She won despite hitting 10 double faults, including four in one game.

 Dutch qualifier Bertens looked as if she was going to take the first set at 4-2 up in the first set and 4-0 in the tiebreak

Williams' French coach Patrick Mouratoglou looks on from the stands as the American progresses to the last-32 in New York